Group by feature not by type: device state tracker

[skulptur]

I think the util directory should have a subdir deviceStateTracker by default with these files:
https://github.com/mediamonks/muban/blob/master/src/app/data/shared-variable/media-queries.json
https://github.com/mediamonks/muban/blob/master/src/app/util/deviceStateTracker.ts

And then we remove data/shared-variable

[ThaNarie]

The idea was to have a common place for sharing variables between JS and CSS, and document that as such. media-queries was just one of them we use by default, there could be others.

If we feel this is not used as much in practice, and can be clearly documented for when it's needed, then i'm fine with (re)moving them.