Create .bl file parser and bottle reassigner

[Klankers]

Presently, CTDCAL doesn't require a .bl file to operate. However, there are instances where bottles are not fired sequentially and these are not accounted for when the .btl-style averages are extracted. Historically, this has been accounted for by manually coding in changes to the bottle number (DMB, P02). Non-hardcoded examples used on GP17-OCE (7345c5e) and ANT (NOT .bl 9aeda3e, rather a PYLON map where multiple bottles closed at one depth).

For this reason, add the .bl files as a sanity check and refer to those bottle numbers for all mean extractions.

.bl file loader & reassigner?

• Alternative to btl_mean() - assemble by btl_fire_on

From a TODO pruned from ctdcal: add improved error handling during bottle file generation.

[Klankers]

Child of #111