Add new keyboard layouts/let users add new layouts

[JakobSuppan]

I use a rather uncommon keyboard layout called NEO 2.0 and i use it with all the tests. However I would really appreciate being able to use this layout with the layoutfluid mode. Idea: let users upload/add their own keymaps using some already used file type (e.g. .keylayout) or add more keyboard layouts, that some users may use.

//Official website of the neo layout: https://neo-layout.org