Add keyboard shortcuts for basic features

[lukebrooker]

This should include:

When translation is being edited

• save as current save state - ctrl/cmd + s
• save as current save state and go to next - tab / ctrl/cmd + enter, enter
• save as needs work and go to next - ctrl/cmd + shift + s, n
• save as translated and go to next - ctrl/cmd + shift + s, t
• save as approved and go to next - ctrl/cmd + shift + s, a
• copy source - alt + c - keep legacy alt + g
• undo edit - ctrl/cmd + z (Kinda already works with default behaviour for me)
• cancel edit - Esc (When available)
• next translation - tab (Save if there is unsaved data) - keep legacy alt + down
• previous translation - shift + tab - keep legacy alt + up
• next untranslated - tab + u
• next needs work - tab + n
• next translated - tab + t
• next approved - tab + a
• next incomplete - tab + i
• next complete - tab + c
• prev untranslated - shift + tab + u
• prev needs work - shift + tab + n
• prev translated - shift + tab + t
• prev approved - shift + tab + a
• next incomplete - shift + tab + i
• next complete - shift + tab + c

Always available

• full-screen/distraction free mode