Make kak more installable

* Kak relies on the kakrc file to be in ../share/kak/kakrc relative
to kak binary rather than in the same directory
* Added an install target to the Makefile
Document installation
Remove unmaintained global.kak
make userconfig: install all kak scripts
update VIMTOKAK
update TODO
CommandManager: use aliases for commands rather than duplicating data

Completion now only proposes full command names