Multiple keyboard (bindingmap) support

[shabble]

Currently, although commands exist to create/destroy keyboards, only a single one is ever created and used (in gui-readline.c:init())

By moving the actual keybindings state into the KEYBOARD_REC object, it should be possible to design an API in which
there are multiple defined keyboards, each with their own set of bindings. A perl API can then create/destroy and switch between
active keybinding maps.

Rationale: Various scripts could benefit from being able to bind keys in a modal fashion, without having to resort to capturing and reparsing gui key pressed each time. Allowing a script to create a new keyboard which has hte desired bindings/functions and
a 'default keyboard' binding to activate it will eliminate most of these issues.