Resolves#25.
Completely refactors the MPD module to be the 'music' module. This now supports both MPD and MPRIS with the same UI for both.
BREAKING CHANGE: The `mpd` module has been renamed to `music`. You will need to update the `type` value in your config and add `player_type` to continue using MPD. You will also need to update your styles.
* feat: more positioning options
Can now display the bar on the left/right, and avoid anchoring to edges to centre the bar.
BREAKING CHANGE: The `left` and `right` config options have been renamed to `start` and `end`
* refactor: major module restructuring
Modules now implement a "controller", which allows for separation of logic from UI code and enforces a tighter structure around how modules should be written. The introduction of this change required major refactoring or even rewriting of all modules.
This also better integrates the popup into modules, making it easier for data to be passed around without fetching the same thing twice
The refactor also improves some client code, switching from `ksway` to the much more stable `swayipc-async`. Partial multi-monitor for the tray module has been added.
BREAKING CHANGE: The `mpd` module config has changed, moving the icons to their own object.
