This does away with `lazy_static` singletons for all the clients, instead putting them all inside a `Clients` struct on the `Ironbar` struct.
Client code has been refactored in places to accommodate this, and module code has been updated to get the clients the new way.
The Wayland client has been re-written from the ground up to remove a lot of the needless complications, provide a nicer interface and reduce some duplicate data.
The MPD music client has been overhauled to use the `mpd_utils` crate, which simplifies the code within Ironbar and should offer more robustness and better recovery when connection is lost to the server.
The launcher module in particular has been affected by the refactor.
This is a first pass towards trying to structure things a bit better, with data generally encapsulated under a single hierarchical tree, rather than lots of globals all over the place. Lots of work is still required.
The plan is that with this and some more work, #291 should become a lot easier to sort.
