Use icons for counters in status bar
Include active requests in the pending requests count.

Counter was 0 if request queue was empty but Picard was still waiting for replies,
with this change, counter is set to 0 only if no active request left.
Reduce spaces between counters.
Remove incorrect author from header.
Merge remote-tracking branch 'upstream/master' into status_icons
Use a green down arrow as download icon instead of globe.

In 16x16 globe is too complex, arrow is much more legible.
Merge pull request #134 from zas/status_icons

Display icons with tooltip instead of text for counters in status bar
Add @throttle decorator to reduce the number of GUI updates
Merge pull request #126 from mwiencek/throttle-gui

Add @throttle decorator to reduce the number of GUI updates
functools.partial is 2.5+
Copy value list in Metadata.update