[Editor] Arrows to move between elements of a group/root when in the different property tabs

Hi Frank,

Just decided to put a few ideas at once.

This one, simply as described in the title... So that is you want to change to colour to a global variable, you don't have to go up a level and down again.

Not sure how complicated vs. useful that could be though, maybe not the highest priority :)

Cheers,

Pierre.