Use getImageName() for labels in bfopen() if present

As pointed out by Allon Klein, when the series name is present in the metadatastore, it should be used in the label rather than auto-generating 'series i/n' .
Add unit tests for the bfopen() function

- Generate fake files, open them with bfopen and check output against fake
parameters.
- Add tests for multi-series, multiZ, multiC and multiT files
Clear data before calling tearDown() method
Merge pull request #557 from sbesson/bfopen_imagename

Read series name in bfopen()