Have IGVSeekableBufferedStream be able to tolerate a negative (ie unknown) stream length

IGV-2038
Further tweaks so that IGVSeekableBufferedStream can tolerate a negative (ie unknown) stream length

IGV-2038
MotifFinderSource tweaks

Set default featureWindowSize = 10MB
default display mode to squished
MotifFinderPlugin enhancements

Add Batch command, unit tests, refactoring to support each
Add unit test for IGVSeekableBufferedStream

Test to see that it can tolerate a negative content length

IGV-2038
Merge remote-tracking branch: upstream/master