Merge add_metadata into master

`add_metadata` adds the remaining logic for the `master` branch to be able to run CR rejection on inputs from all six detectors. The pipeline now accepts `_flt.fits` files, in addition to `_c0m.fits` files. 

CR rejection is run on WFPC2, HRC, WFC, and UVIS using parameters acquired from files unique to each detector in `MTPipeline/cosmicx_cfg`. For HRC, WFC, and UVIS, the readnoise and gain are read from the image header files and supplant the readnoise and gain set in the configuration files. CR rejection is not run on IR or SBC images. We are confident that no CR rejection is needed for our IR data, and the same likely holds true for SBC (though not for the same reason). At the moment, the `cosmicx` parameter files for IR and SBC remain, but can in the future be removed (although this will require changes into `get_cosmicx_params`).