Fix DefaultUploaderService#installUploader()

We used initialize() to force a re-discovery of all available
uploaders after installing an uploader, but that code changed now:
initialize() no longer discovers all the uploaders; uploadMap()
does. And hasUploader() calls uploadMap(). So all we need to do now is
to make sure that the DefaultUploaderService forgets what uploaders
it knows after installing a new uploader so that the lazy code can
kick in.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Update to scijava-common 1.5.0

Changes include:

* The pom-scijava version was bumped to 1.52, which is pinned to
  scijava-common version 1.5.0.

* The PTService class hierarchy moved upstream to SciJava Common, so
  those classes have been removed from ImageJ, and package names changed
  in the import statements.

* The org.scijava.service.Service interface gained another method,
  registerEventHandlers(), which is normally taken care of by
  AbstractService, but we have a couple of direct implementors.
  So this commit adds method implementation stubs for those.