Make gui tooltips referring to key assignments dynamic

That is, make them not lie when keys are reconfigured.

Fixes #1914
Hotkey "translation" table for displaying keys

Refs #2189
Display hotkey glyphs instead of Fife key names in dynamic tooltips

This helps achieve less ugly and generally shorter text, which is good
to have in a tooltip.
When some action is not assigned at all, we display "Unassigned" which
is very long, but in that case clarity is rather important so that
nobody looks for keys with names similar to whatever abbreviation of it.
Merge pull request #2189 from unknown-horizons/1914

Make gui tooltips referring to key assignments dynamic