Regression introduced by recent GTK refactor.
The `glib_recv` macros previously using the passed in expression as the receiver, which was causing a new receiver to be created *every* time an event was received. This caused some peculiar behaviours where some events just never got through if sent too close to each other.
This was most obvious in the `workspaces` module.
Fixes#381
This is a major refactor which updates GTK, GLib and GTK Layer Shell to their latest versions.
GLib channels, previously used for receiving events on the GLib Main Context thread have been deprecated and a new method for running Futures on the main thread has been added instead. This commit also replaces all the deprecated code with this.
As part of the above, a bug was uncovered related to creating the GLib main context inside the Tokio runtime. Spawning of Tokio tasks has been refactored to fix this.
