#13 Support reloading configuration without restarting

With #11 partially implemented as of fc0196f697, I really want to be able to run systemctl --user reload kaylee to reload configuration without restarting Kaylee. This is a good idea in general: it also paves the way for GUIs having a configuration window which applies changes without restarting. As this issue immediately feels like “systemd unit part 2”, I’ll work on it as soon as I close #11, which I’ll probably get to tomorrow.

I didn’t realize at first just how much design this issue requires. The main consideration that I can’t decide is what we should do with values provided by command-line arguments when reloading configuration. Should they still override the configuration file, or should the new configuration file override them? Neither option seems like a good idea to me, as each would result in some options not being set the way a user might expect. It almost seems then that the command-line options should be removed entirely, but that doesn’t seem like a good idea either as I use a couple of them regularly.

I am undecided on this issue. It would be nice to be able to reload configuration without restarting, but I doubt it would save much time over restarting. The awkward design position it creates makes me feel that this feature should be dropped from the 0.2 release. Moreover, it should probably be closed until a decision can be reached about the design involved, which may take indefinitely long.