use managed jdom version
handle MissingViews in AbstractSpimSource
parallelize hdf5 export:
* 1 thread is responsible for writing data blocks to hdf5. It maintains a
  bounded queue of blocks to be written.
* n threads prepare blocks by copying or downsampling from the input image,
  submitting completed to the write queue. Processing of the next input
  image may start before all blocks of the previous image were written.
put public WriteSequenceToHdf5 methods to the top of the file and add missing javadoc