Add distinction between movement and letter keys

[argothth]

Fixes #732

• Add a condition to check whether the pressed key is a symbol or movement key in matches_keypress
• Update the execute function to match the signature of matches_keypress

Test ran:

1. With my custom keyboard layout, I opened Minder;
2. I pressed Enter on the root node to validate that text is saved;
3. I pressed E (which is also up arrow key for me if I press AltGr) and successfully edited the text.

[phase1geo]

Thank you for the improvement PR. Nice improvement!

[argothth]

Thanks for merging it :))