LIMS-697: Use more specific PVs for puck names

[ndg63276]

Github issue: #53
JIRA ticket: LIMS-697

Summary:

@jlmuir points out that not all facilities have a one-to-one mapping of beamlines to pv prefixes (DLS included). As the $bl_pv_map variable is only used in one place, we should replace it with a template for the specific PVs it is used for.

Changes:

• Remove $bl_pv_map variable
• Remove DLS-specific hardcoded PV names
• Add $bl_puck_names variable for a template for the puck names PV

To test:

• Go to the assign container page for a visit (eg /assign/visit/cm37235-1) and check the loaded pucks are displayed next to the puck number (eg CPS-0001 below)
  

[gfrn]

I think the way PV searches are done (build PV name array, then mass caget, and reindex, searching for the returned PVs in the initial array) feels a bit off, but I cannot say with absolute certainty it can be refactored without affecting other bits of code elsewhere.

Also, long shot, but EPICS exposes EPICS_BASE and EPICS_HOST_ARCH, so if we really wanted to, we could also build the path from these environment variables rather than from a path to caget in config.php, but that's minimal