InteractiveCommand handles events off EDT

All InteractiveCommands event callback methods will now be executed on a
non-EDT thread. This ensures these methods will be able to perform
dispatch operations, such as sending status messages via the
StatusService. Without this change the EDT would deadlock.
Widgets now refresh off the EDT

All UI-based widget implementations will now run their refreshWidget
methods off the EDT. This will allow those methods to perform dispatch
operations, such as sending status updates via the StatusService (which,
if launched from the EDT, would deadlock).

To accomplish this, added an AbstractUIInputWidget layer to mark widgets
that are UI-specific and spawn new threads if a given widget is a part
of a UI that uses the EDT.

he UserInterface interface was modified with a flag method indicating if
a UI implementation requires the EDT or not.

All UI implementations were updated as appropriate, and all
AbstractUIInputWidgets shifted their refreshWidget implementations to
doRefresh (the public refreshWidget is now the gateway method where
thread-safety is checked).
Added MinMaxMethod

New interface: MinMaxMethod for computing min/max values in a given
interval. The default implementation wraps the imglib ComputeMinMax
class but injects context-based status reporting. The
DefaultAutoscaleMethod now uses a MinMaxMethod instead of ComputeMinMax.
Merge branch 'threadsafe-min-max'

Updated UI widgets and interactive command callback methods so that refresh and
update methods are no longer called from the EDT unless they do not use the
EDT. This allows these methods to perform dispatch operations such as sending
status messages.

Taking advantage of these framework changes, included is a MinMaxMethod forked
from ImgLib that can now report its progress via the StatusService.