feat:Add support for tabs in keyboard shortcuts

[Davidy22]

Also changed the default keybinding for next/prev tab. Had to rewrite half of the keybindings code to make this work, but the incidental refactor along the way was pretty good too.

Resolves #152

The keybinding rewrite is hefty, testing before merging preferred, I'll keep using it for now, haven't noticed anything off between finishing the code and creating this pr.

[besworks]

I just updated my guake install (previous version was only from back around July) and I think something about this PR may have broken my customized keyboard shortcuts which use the super key. Every time I try one the letter I pressed just gets output to the terminal. Other shortcuts I have which do not use the super key still work, and remapping the broken ones also works. Is it just me or can anybody reproduce this behavior?

Update: Apparently if I have an additional modifier like alt or shift then the shortcut works but just super+key doesn't.

[Davidy22]

#1941 has been created to fix this, and I'll create a new release once it gets merged. Can't approve and merge my own pull requests, so waiting on @mlouielu to approve or for @gsemet to release more privileges to us.

[besworks]

Oh! Great! Thanks for letting me know. I didn't see that when I searched. I will wait for your fix.

Also, thank you for implementing Tab key support in the shortcuts. It's very nice to be able to Ctrl(+Shift)+Tab like in most other apps. 👍