Add macOS TouchBar integration

[arlolra]

For #1681

[scottnonnenberg]

Thanks for doing this proof of concept, but I'm not convinced we need to do anything here yet.

[arlolra]

😢

[GhostLyrics]

If this enables macOS's buildin spellchecker as a side effect I'm inclined to disagree. The upside of that one is that it can guess the language in use from the context if you have more than one language enabled (e.g. English and German for me).

[snuffels]

Touchbar support works. The correcting of spelling on the touchbar works a bit strange.
Lets take this sentence

Waht are the fetures of this sotware pakage?

and I go back to correct the words I get this:

What are the features tures of this sotware package e?

Waht was easily corrected but it addded an extra space in the end
after clicking on a couple of places fetures could be changed but it corrected the word before the cursor and added a space and left the rest of the word as it was.
It could not find a solution to sotware, thats an apple problem
And after klicking on a couple of places of pakage it came with the correct word but only changed the word before the cursor and added a space and left the 'e'.

Can this be fixed?