WIP: snapshot dependency

replace with an updated imglib2, with different calibration support for
ImgPlusses.
ImgOpener: only add calibration if axis length > 0

Updated the ImgOpener calibration logic. If an axis length is <= 0, the
calibration should not be retrieved (or set) as the axis may not exist.
If the size is 1, it's currently a real axis.
ImgOpenerTest: test ImgPlus calibration

Added a test to verify calibration values are preserved when using
ImgOpener to create an ImgPlus.
WIP: Add SCIFIOService

NB: Contains snapshot dependency. Remove before merging with master

Adds a SCIFIOService interface, which all io.scif.* services now
extend. This allows for convenient Context creation by just specifying:
new Context(SCIFIOService.class), for example, without creating an
explicit list of services.

Removed TypedService, as it's now obsolete and SCIFIOService seems
better named.
AbstractImgIOComponent: update service list

Instead of using an explicit Service list when creating a new Context,
use SCIFIOService.class and ScijavaService.class.

This is a much more flexible notation that alleviates the need for
maintenance of this list.