Inherit mappings

[sezanzeb]

@kermitfrog has brought up an interesting point:

Also in inputmangler, mappings can be inherited - I don't think that can be currently represented in input-remapper.

(kermitfrog/inputmangler#2 (comment))

preset configs could have a "parent_preset_path" property, which is then resolved and merged into the current preset. My intuition is that this wouldn't be that hard to implement. The resolving and merging shouldn't happen for the gui though, only when the service loads a preset

The gui would need some sort of dropdown to select a parent preset somewhere.

This makes it easier to copy the same preset to multiple devices