vk-driver: Generate most keymaps on the fly

Instead of hardcoding a de and other keymaps rather build it from the needed symbols on the fly. This needs some quirks for electron apps but with this I get all of the Ukranian symbols working nicely. This is based on the dynamic keymap generation we introduced in !96 (merged).

Since we don't need the system keymaps anymore we can use the fallback keymap we ship anyway for the terminal layout and make that very explicit (we could even look into generating that too at some point - this would allow for e.g. different base languages). While at that at the few remaining characters that didn't yet work in vk mode.

#19 (closed)