Create small test datasets

[mwakok]

It would be good to have small datasets that we can use for quickly testing the data handling functions.

• [x] Small dataset for each filetype (.tif, .tiff, .nd2, .lif)
• [x] Stack of about 10 frames
• [x] In the case of .lif, a dataset with one and multiple experiments
• [x] All etadata should be preserved