Add "all" and "none" buttons

[mzur]

In the dismiss step: "Dismiss all/no annotations"
In the re-label step: "Re-label all annotations with the selected label"/"Re-label no annotations"

This can be useful in a two step annotation process. In the first step users only mark all interesting things with a single label ("Interesting"). In the second step they use Largo to sort the interesting things into their specific label categories. They select e.g. all starfishes in the dismiss step of Largo and then re-label all of them as star fish. With these buttons you don't have to re-label each annotation individually.