example data and unit test added

[Tomnl]

• Added a single mzML file from each MTBLS study up till 02 Aug 2018 and stored in a compressed file. Each file has the binary removed so that we can store in github without taking up too much space
• Added example JSON output for the files above (example_files/MTBLS-no-binary.tar.lzma)
• Added simple unit test to check the metadata from the files above (example_files/MTBLS-json-meta)

Note: this replaces the previous pull request where the json data was not in a compressed and archived format https://github.com/ISA-tools/mzml2isa/pull/34

[Tomnl]

Going to merge this now. The core code has not been update at all so any new updates should not affect the example data and the simple uni-test