Add unit tests for assay app plugins

[mikkonie]

We recently added tests for study app plugins, but assay plugin tests are still missing. Especially with #1946, which gives user a greater freedom to modify how assay links are rendered, these tests become quite necessary.

I'll set up a base test framework as per usual and work from there.

NOTE: Where applicable, test ISA-Tab files should be added to the repo as unarchived files instead of zip archives. Existing data should be similarly altered. Binary blobs shouldn't be committed unless necessary (documentation figures etc).

Taks

• [x] Add tests for cytof
• [x] Add tests for dna_sequencing
• [x] Add tests for generic
• [x] Add tests for generic_raw
• [x] Add tests for meta_ms
• [x] Add tests for microarray
• [x] Add tests for pep_ms

[mikkonie]

Done.