LOFAR reader hotfixes

[MijnheerD]

This PR contains a bunch of small hotfixes for the LOFAR branch:

• The TBB reader now raises an IndexError when the endpoint is off the end of a file
• TBB files from remote stations are now skipped when globbing over the directory (solves crashes involving events with only remote TBB files)
• The channel group IDs are now int instead of str (for consistency with Detector description)
• After reading in the channels, we now check whether both channels from the flagged group IDs are removed from the station
• The calibration delays can now be retrieved from the readLOFARData object as a dict, ensuring the calibration delays are associated to the correct channel ID

[anelles]

Code looks good from my side, but I haven't tested this.
I assume you tested that it works.
Feel free to wait for LOFAR core team to review in independent cross-check, but you the ok to merge already.