[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 this purpose

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.