Add information on reference files used to calibrate exposures

[bhilbert4]

@mperrin just created a tool to check the header of a given exposure's file, and query CRDS, and return information on the reference files used to calibrate the exposure. @hover2pi noted that this could be useful information to have in JWQL.

He suggested linking the info to the reference file names when you open the header. Another option would be to add a new button next to the "Display Header" and "Explore Image" buttons that would bring up information on all of the reference files.

See the original conversation for details, along with an example notebook and code.

[bhilbert4]

JWQL now shows some header info on the exposure level pages, including the CRDS context used to calibrate the data.