Fix bad beam monitor ID error message

Apparently, the Mantid logger won't print error messages unless they end
with a newline char.  Had to add one to the bad beam monitor ID error.

Refs #9563
Update handling of beam monitor packets

Fix 2 problems with how beam monitor packets are parsed:
1) Properly deal with the case where a packet has no actual events
2) When checking to see if we'd reached the end of the packet, the code
was including the size of the packet header when it shouldn't have.

Refs #9563
Get event data from beam monitor packets

Added functions to retrieve event TofF and other data from the beam
monitor packets.  Removed the firstSection() function because
it wasn't really needed.

Also, some indendation cleanup (tabs vs. spaces)

Refs #9563
Merge branch 'feature/9563_beam_monitor_packets' into develop