Add support for tab/backtab navigation.

[danhper]

I made a small change to allow to navigate through the results using tab/back tab.
I do not think tab should be useful for anything else in the input context anyway, so
this should not interfere with current functionalities.

[benfalk]

This is awesome, I am going to pull it into my repo while I wait for it to get merged. 👍

[danhper]

@benfalk Glad it can help!
If you (or anyone) is interested, I also implemented emacs navigation in my fork:
https://github.com/tuvistavie/Mutate/tree/emacs_navigation
It can be activated by adding Layout=emacs in the default section.
I wanted to send another PR, but as this one does not get merge I am waiting for now.