Add support for ctrl+{backspace,delete} to remove words in text inputs

[norohind]

Hi. Pressing ctrl+backspace or ctrl+delete in order to delete a word to the left or to the right of the cursor is a pretty common thing when working input fields, at least for me. I was expecting for this thing to work in supersonic too.

[dweymouth]

Oh yeah, this is definitely a good one to add, but it has to happen upstream in Fyne - fyne-io/fyne#4524

I could probably implement this for the next Fyne release after which it could end up in Supersonic in maybe 1 or 2 releases from now

[dweymouth]

On a separate note, I've been working on keyboard-based scrolling and focus navigation of the list and grid views, so keyboard usability of Supersonic will get a big bump next release :)