[keyboard layouts] distinguish entries

Reference to xbmc#5472
and agreeing that the full language name + layout becomes a long-winded
string to have in the button on OSK

@stefansaraev suggested on irc something like xbmc#5326 seems to add support for similar idea. though I suspect my assumption is incorrect)

<layout name="English ABC" id=eng abc>
<layout name="English QWERTY" id=eng qwerty>

So this assumes #5326 is merged and assumes that the codingtable can be used for the purpose the id as above would be same or if more code needs to be added to do this.

The idea is the list selection would display the <layout name> and the button label would display the <codingtable> entry under
this would be ideal.

I've added a small comment to the xml to serve as minor documentation so all future additions
consider following some predefined "standard" sensible and logic.