ReaderFilters - fix closing/cleanup

ReaderFilters were closing parent readers, but not properly closing
themselves. This was especially confusing as many filters implemented
their own cleanUp method, which was called from an overridden close
method.

Refactored to move close behavior to AbstractReaderFilter, which now
always calls a helper cleanUp method (instead of separately defining it
each time as needed). This now ensures that ReaderFilters are closed
properly.
SCIFIOCellImg closes the reader upon disposal

SCIFIOCellImgs are odd cases in that they need to remain open for the
full life of the ImgPlus they are attached to, to allow dynamic loading
of plane regions.

To facilitate this, a SCIFIOCellImgCleaner was created, and
SCIFIOCellImgs now register themselves for cleanup on creation.

SCIFIOCellImg and SCIFIOCellImgPlus also both now implement disposable,
allowing manual disposal.

Closes #128
config package-info: remove trailing newline

Minor formatting cleanup