Add ability to create layer aliases in the json defs.

Some keyboards use layers to define certain feature sets, specifically kb's with dip switch functionality.

It would be nice to be able to add UI aliases to the layers so that the app show the alias instead of the "[0][1][3][4]".

I would envision this to only be relative to the UI ... underlying protocol and QMK needs no changes. The json file could have something like this (example only):

{
"layer_alias": [
"0": "Mac",
"1": "Mac-Fn",
"0": "Win",
"1": "Win-Fn"
]
}

The UI would then show: [Mac][Mac-Fn][Win][Win-Fn]