[xkb] create a Python installer output

[fabi1cazenave]

Installing kalamine might be too cumbersome for some users, and I think a Python installer would be a better fit for most end-users.

It might be a bit of a hack but I think kalamine could pick some code from xkb_manager.py along with an XKB string to create a standalone installer, like the one used for Qwerty-Lafayette.