Enable reading of CRAM Header with no (explicit) reference

[yfarjoun]

Description

fixes #731 by allowing a CRAM file to be opened using a trivial referenceSource which has been added to the SamReaderFactory default settings.

• added test cases to show that DictionaryExtractor works and also that reading the header of a cram file works.
• fixed old tests that broke as they were getting a new (=unexpected) exception when opening a cram file for reading without a reference.
• continued the march of java8 into the code
• suppressed some intelliJ code inspection warnings and fixed a javadoc error.

Checklist

• Code compiles correctly
• New tests covering changes and new functionality
• All tests passing
• Extended the README / documentation, if necessary
• Is not backward compatible (breaks binary or source compatibility)

[coveralls]

Coverage increased (+0.005%) to 69.745% when pulling b74b332 on yf_make_get_header_possible_from_cram_with_no_reference into 58f4154 on master.

[cmnbroad]

@yfarjoun I think this will mask the fallback chain thats in place in the default reference source implementation (the code that uses environment variables to try the ENA download service or DEFAULT_FASTA settings - I don't think we have tests for those). Its currently established through the calls in SamReaderFactory to getDefaultCRAMReferenceSource. When we switched to using an interface based pattern for reference source for IGV, I intended to break those out into a separate implementations for each type (ENA ref service, DEFAULT_FASTA, user-supplied file) so we could establish which one to use once up front, but never did. For now they're still all mashed together in the one implementation.