This is the first commit of a new API to add and remove buttons
and keys from clients. The goal is to get rid of the default `rc.lua`
"hardcoded" list of client buttons and keys to allow modules to modify
the defaults. This is part of the larger effort to make `rc.lua`
modular.
Another step in moving these APIs toward the common object oriented and
declarative paradigms used by other APIs.
This commit introduces the `awful.keyboard` module. It currenly only
exists as a placeholder for the first few append/remove function, but
will grow in scope in another pull request to expose the currently
private modifier APIs and to provide keybindings collision detection
and replace some of `awful.hotkey_popup` business logic.
The `keygrabber` tests which uses root keybindings are disabled for
now to keep the commit size small. This is necessary since the shims
will need many iterations of changes before this work again with the
new syntax.