Add hack for composite image construction

Created CompositeImageFixer class which ensures C,Z,T dimensions are
preserved when constructing a new CompositeImage.

Workaround for the fact that if there are less than MAX_CHANNELS slices
of a stack, all dimensions are converted to channels by the
CompositeImage constructor.
Merge pull request #4 from fiji/composite-image-hack

Add hack for composite image construction