HDF5-based wrapper for LOFAR datasets

[griffinfoster]

Currently the LOFAR ACC and XST files are just binary blobs with limited meta-data in the file name. It would be useful to create an HDF5-based wrapper to contain the visibilities and meta-data such as station id, subbands/frequencies, rcu mode, time, integration length, antenna positions, uvw positions.

Once this is established, the scripts can be updated to use the new format.

[griffinfoster]

This will be supported by an external module (https://github.com/griffinfoster/issformat). Support for this interface needs to be added now.