Need to add more smoke tests

[mkuhring]

For each of the important use cases, we should have a test data set that is just parsed and it is ensured that

1. the file parses without crash
2. the right number of studies and assays is created
3. the number of materials, processes is correct
4. the number of material and process attributes is correct

All of this information can be easily provided and leads to concise tests. These are smoke tests only.

[mkuhring]

@holtgrewe: Can we consider this done with the all writing tests (#40)?

[mkuhring]

Need to add sample sheets from Manuel.

[mkuhring]

@holtgrewe you wanted me to add some of your ISA-tabs for testing. This can be quickly done, just send me data when you have time. But nothing confidential of course.