New BlackrockIO interface

This pull request adds a new implementation of the IO for Blackrock files. The IO extends the functionality of the previously available one by allowing to read also spike and event data besides analog signal data. The main functionality not yet implemented in the rewrite is the ability to write Blackrock files.

The previous IO was moved to blackrockio_deprecated.py, for compatibility reasons, and until write functionality is integrated into the new IO.

The IO comes with two IO specific unit tests based on a data set provided by Blackrock Microsystems (uploaded to GNode portal with permission). One tests for input parameter handling, and one compares the loaded data to data loaded using a matlab implementation provided by Blackrock Microsystems.