Update keybindings while Penrose is running

[midnightexigent]

Is your feature request related to a problem? Please describe

Currently the keymap is read once at init and is used for the entire lifetime of Penrose. For alternative keyboard layouts, this means that setting the keyboard layout in a file like /etc/X11/xorg.conf.d/00-keyboard.conf doesn't work #165

So, any updates to the keymap will not be reflected in the Penrose keybindings

Describe the change / addition you'd like to see made

Listen for changes to the keymap and update the keybindings accordingly

[midnightexigent]

Update: I just noticed that when using a display manager (eg. LightDM), the files are executed in the correct order: /etc/X11/xorg.conf.d/00-keyboard.conf is sourced before Penrose runs.

This can be an alternative to the quick and dirty solution in #165 (ie. adding setxkbmap <map> in .xinitrc)

[sminez]

A long time coming but this should now be implemented as of the commit above. The rewrite to the 0.3 API actually made this pretty much trivial to implement in the end but I missed it at that time. Sorry!