Added signatures for populating ImageMetadata

SCIFIOMetadataTools now has more options for populating Metadata,
including the ability to automatically look up bits per pixel of a given
pixel type.
AbstractMetadata only resets SCIFIO fields

The AbstractMetadata method will now only reset instances of
ome.scifio.Field.
ChannelSeparator checks plane compatibility

Was mistakenly using the ReaderFilter#isCompatible method, which
determines if the Filter is capable of wrapping the given object (e.g. a
Reader) and thus would always be false when testing a plane.

Now just test to see if it's an instance of a ByteArrayPlane.
Created SCIFIO Cell package

The SCIFIOCell series of classes facilitate creating an imgplus
(SCIFIOImgPlus) that uses the CellImg principles of dynamically loading
pixel information as it's requested.

Cells allow an image to be broken down into manageable bits, so that
images too large for memory can still be viewed and operated on.

The SCIFIOCellCache performs actual caching operatings, allowing
operations on cells to persist after the cell falls out of scope. It
uses an in-memory weak reference cache for fast memory action, and an
Ehcache back-end for its disk caching capabilities (and general memory
management).

This change also involves migrating ImgOpener and ImgSaver from Imglib
to SCIFIO (as these classes use SCIFIO to perform their IO operations,
and SCIFIO uses Imglib).