Morphology framework TODOs.

[tinevez]

After the merge of PR #2, the following tasks were noted to be done:

• RectangleShape and CenteredRectangleShape should be unified and support for non-symmetric neighborhood should be added. This can all be the same class with a bunch of more constructors.
• The xxxNeighborhoodLocalizableSampler classes share a lot of code. There is potential for unification there. We could make xxxNeighborhoodFactory implementations non-static and have them contain all the parameters required to construct the neighborhoods. Then there could be only one NeighborhoodFactory and one generic typed NeighborhoodLocalizableSampler that is used everywhere.
• The xxxShape.NeighborhoodsAccessible.randomAccess( final Interval interval ) should make an effort to compute the interval of the source that is required (i.e., output interval plus border depending on the strel bounding box) and request a source RandomAccess for that required interval. This will allow Views to make better choices of whether it can strip away extensions in transform chains. Also in some cases it is required to actually enforce the extension for extended-and-then-cropped views. See javadoc added in imglib/imglib2@3569f58 for additional explanation. (I (Tobias) would suggest to postpone this until after the previous item has been addressed because all required logic is in the RectangleNeighborhoodLocalizableSampler already.)