Mount problem data (SICK, FraCaS, SNLI) as volume

[XanderVertegaal]

There is already a seed volume definition, but there are no data files in it yet.

https://github.com/CentreForDigitalHumanities/langpro-annotator/pull/87/changes/044eee3d314d26d82d50457d00d9d5dc78fa368f..0538d9c06e6034120593683f5c257fcc4f53b52d#diff-e45e45baeda1c1e73482975a664062aa56f20c03dd9d64a827aba57775bed0d3L49

[jgonggrijp]

I think I intended that as a directory that was ignored by Git, in which the developer could place problem data in order to inject them in the containers. Just to clarify why it didn't contain the data yet.