OCSADV-191: pass an obs context to the magnitude table lookup instead of creating the magnitude table with an obs context
OCSADV-191: thread the MagnitudeTable through all the code that ultimately needs it
OCSADV-191: add parsing of probe limits from a file, loading magnitude table at startup
OCSADV-191: switch to the config file based mag table
OCSADV-191: separated the GeMS-specific behavior in DefaultMagnitudeTable to GemMagnitudeTable, deleted DefaultMagnitudeTable, delegated to GemsMagnitudeTable where necessary.
OCSADV-191: minor cleanup
OCSADV-191: handle empty entries in the spreadsheet
OCSADV-191: switch to probe limits downloaded from spreadsheet
OCSADV-191: log exceptions
Merge pull request #90 from swalker2m/feature/OCSADV-191

OCSADV-191: configuration by magnitude table.  Merging for continuing work on AGS.
OCSADV-170: If guide star is missing magnitude for required band, the problem is marked specifically as a warning in the guiding feedback, and the P2 check and QPT analysis translates these to warnings instead of errors.
Revert "OCSADV-170: If guide star is missing magnitude for required band, the problem is marked specifically as a warning in the guiding feedback, and the P2 check and QPT analysis translates these to warnings instead of errors."

This reverts commit c38e2e4920d121b5f0bcdebf42be7131f9281ab9.
OCSADV-23: Removing UNBOUNDED from PosAngleConstraint list since it will not be supported for Dec 2014 release.
OCSADV-23: Changed variable name for clarity.