Accept Table objects or user files

[AnthonyHorton]

Adds option to accept either astropy.table.Table objects or a path to a user data file for the throughput, transmission or QE data when creating Optic, Filter or Camera objects.

This makes it significantly easier to use gunagala for instruments not defined in the built in performance.yaml config file.

[coveralls]

Coverage decreased (-0.02%) to 90.126% when pulling 8375432 on local-data into 5cfc1c3 on develop.