Add shortcuts panel

[ollimeier]

This is a draft PR for early feedback.

Based on our meetings (yesterday and today), I reworked a couple items:

• undo/replace ui-form code changes with custom made code
• set default shortcuts for tools back to 1234567
• remove editing of globalOverride in UI and dialog
• a different solution for the "delay recoding" of a shortcut
• add export/import of shortcuts (via json files)
• merge the two 'undo' shortcuts into one, even though there are internally two (one with and one without globalOverride)
• open dialog via double click on input element (not on label as it was before)
• added delete and refresh button next to the input element (only visible if shortcut input is focused)

Open issues (I still have not found a solution, yet):

• the refresh and delete svg icons are not shown (currently displayed with green boxes)
• the shortcuts are not displayed correct in the menu (this seems to be a loading issue)
• tooltip does not work for label nor for input element, but it works for the icon-buttons, which is weird.

[ollimeier]

I am closing this, because I will open a new draft PR in a bit (based on the new 'actions'-approach).