Make navigating Mask To List easier

[linojon]

The Mask To List widget gives a list of all frames that use a mask. What i'm doing is, I modified a mask and i want to check each frame that uses the mask to see if there's now more than 0 same frames on any of them e.g. the mask is still unique for frames i already did. Currently this is very mouse intensive having to click each item in the list one at a time. It would be convenient be able to make each frame in the list "selected" using the arrow keys as i navigate through the list.

[zesinger]

I will add a button to change the selection to all the frames using the current selected mask.

[zesinger]

Done