WIP: Use the updated imglib2-meta project structure

This is a WIP because it needs some more changes squashed in to make
sure it still compiles.
It also needs the imglib2 version bump squashed in, or else it won't
compile (it only works for us locally now because of local hacks to
pom.xml: imglib2.version -> 2.0.0-SNAPSHOT).
WIP

Next steps:
- CalibratedSpace -> OldCalibratedSpace

Squash all that into the conversion commit.
Still must be a WIP, because eventually we have to
squash the imglib2 version bump into there too.

NEXT commit after minimal API updates:
- CalibratedInterval -> CalibratedRealInterval
- CombinedInterval -> CombinedRealInterval

This second commit will update the ImageJ2 codebase to actually *use*
the new img-metadata features, instead of just using the backwards
compatibility stuff (e.g., OldCalibratedSpace).