Updated getDimTypes to match getDimLengths

The ImgOpener#getDimLengths method should now return dimension labels
that match the lengths returned by ImgOpener#getDimTypes.
Corrected ColorTable population for PlanarImgs

When reading plane data for PlanarImgs, the reader metadata was
mistakenly being checked for a color table.

This was always false, because the reader filter was always wrapped with
a ChannelSeparator that prevented the underlying Metadata from being
examined.

Also, because the plane was just read, its color table was readily
available and is now used instead.
Merge branch 'ImgOpenerFixes'

Two fixes for ImgOpener:
* PlanarImgs should now populate their ColorTables correctly
* The AxisType[] returned by getDimTypes should now match the size and ordering
  of axis lengths returned by getDimLengths.
Fixed TIFF format priorities

MinimalTIFF and TIFFFormat were being placed at the same priority, which
was causing MinimalTIFF to be sorted ahead of TIFF because M<T.

Corrected this by adding explicit constants in each class that uses
priority more than once, with TIFF/OMETIFF each adding 1 to MinimialTIFF
priority. TIFFJAI is now MinimalTIFF - 1 (instead of TIFF - 1, which
would be equal to MinimalTIFF).