fix 1601

[ammen99]

This PR is an attempt at fixing #1601.

The solution is a bit more generic than that, though: we allow generic activators in the config file. Then, a plugin needs to parse them and activate them instead of core.

Fixes #1601

[ammen99]

Example config:

[core]
plugins = xkb-bindings expo ...

[expo]
toggle = Mod4+e | <super> KEY_J | ...

In other words, the xkb-bindings plugin extends the available activator types with a new syntax which resembles Sway's and other compositor's a bit more closely. It also uses xkb to resolve keycodes to keysyms first, i.e the e in the example is not equivalent to KEY_E, but depends on how it is mapped exactly by the current layout. If you for example switch to a cyrillic layout (or anything else) then the binding stops working, because then KEY_E is mapped to a cyrillic letter which has a different keysym.

I'm open to feedback from the people who requested this feature, let me know whether this is what you had in mind.