BUG: Only thread 0 should report progress.

The progress update observer is frequently used to update GUI
progress. The progress should only be updated by the main thread,
otherwise this common uses will segfault with the gui update.

The LabelMapFilter was updated with a manual update to the filters
progress, additionally the abort status is also check.

Change-Id: I1540ee5785a26b196524f51ac604d3bfcd18d0b0
Merge topic 'LabelMapOnlyMainThreadReport2'

1d5dfb2 BUG: Only thread 0 should report progress.