Use the adjustments for updating V and I

There's not much reason to use the widgets themselves when I can use the
model instead.

data/pd-buddy-gtk.ui

   </object>
   <object class="GtkAdjustment" id="current-adjustment">
     <property name="upper">5</property>
-    <property name="step_increment">1</property>
-    <property name="page_increment">10</property>
+    <property name="step_increment">0.10000000000000001</property>
+    <property name="page_increment">1</property>
+    <signal name="value-changed" handler="on_current_adjustment_value_changed" swapped="no"/>
   </object>
   <object class="GtkAdjustment" id="voltage-adjustment">
-    <property name="upper">20</property>
-    <property name="step_increment">0.01</property>
+    <property name="upper">21</property>
+    <property name="step_increment">0.10000000000000001</property>
     <property name="page_increment">1</property>
+    <signal name="value-changed" handler="on_voltage_adjustment_value_changed" swapped="no"/>
   </object>
   <object class="GtkApplicationWindow" id="pdb-window">
     <property name="can_focus">False</property>
                                                 <property name="can_focus">True</property>
                                                 <property name="width_chars">5</property>
                                                 <property name="text" translatable="yes">0.00</property>
+                                                <property name="xalign">1</property>
                                                 <property name="input_purpose">number</property>
                                                 <property name="adjustment">voltage-adjustment</property>
                                                 <property name="digits">2</property>
                                                 <property name="numeric">True</property>
-                                                <signal name="value-changed" handler="on_voltage_spinbutton_changed" swapped="no"/>
                                               </object>
                                               <packing>
                                                 <property name="left_attach">1</property>
                                                 <property name="can_focus">True</property>
                                                 <property name="margin_left">12</property>
                                                 <property name="width_chars">5</property>
+                                                <property name="xalign">1</property>
                                                 <property name="input_purpose">number</property>
                                                 <property name="adjustment">current-adjustment</property>
                                                 <property name="digits">2</property>
                                                 <property name="numeric">True</property>
-                                                <signal name="value-changed" handler="on_current_spinbutton_changed" swapped="no"/>
                                               </object>
                                               <packing>
                                                 <property name="left_attach">1</property>

pd-buddy-gtk.py

 
     def on_select_list_row_activated(self, selectlist, serport):
         # Get relevant widgets
-        voltage = self.builder.get_object("voltage-spinbutton")
-        current = self.builder.get_object("current-spinbutton")
+        voltage = self.builder.get_object("voltage-adjustment")
+        current = self.builder.get_object("current-adjustment")
         giveback = self.builder.get_object("giveback-toggle")
         pd_frame = self.builder.get_object("power-delivery-frame")
         output = self.builder.get_object("output-switch")
         # Set visibility
         rev.set_reveal_child(self.cfg != self.cfg_clean)
 
-    def on_voltage_spinbutton_changed(self, spin):
-        self.cfg = self.cfg._replace(v=int(spin.get_value() * 1000))
+    def on_voltage_adjustment_value_changed(self, adj):
+        self.cfg = self.cfg._replace(v=int(adj.get_value() * 1000))
 
         self._set_save_button_visibility()
 
-    def on_current_spinbutton_changed(self, spin):
-        self.cfg = self.cfg._replace(i=int(spin.get_value() * 1000))
+    def on_current_adjustment_value_changed(self, adj):
+        self.cfg = self.cfg._replace(i=int(adj.get_value() * 1000))
 
         self._set_save_button_visibility()