Add LoaderConfig plugin to the Reference Viewer

[ejeschke]

The LoaderConfig plugin allows you to configure the file openers that can be used to load various content into Ginga.

Registered file openers are associated with file MIME types, and there can be several openers for a single MIME type. A priority associated with a MIME type/opener pairing determines which opener will be used for each type--the lowest priority value will determine which opener will be used. If there are more than one opener with the same low priority then the user will be prompted for which opener to use, when opening a file in Ginga. This plugin can be used to set the opener preferences and save it to the user's $HOME/.ginga configuration area.

Documentation added and change log updated.

[ejeschke]

If/when you have time, @pllim.

[ejeschke]

Previously, the loader preference could only be set by using the --fitspkg command line option or the FITSpkg setting in general.cfg. These methods still work, and use the loader priority apparatus, as before.

[pllim]

@ejeschke , I probably won't have time till next week at the earliest. I also have not been using this feature much, so not sure how best to contribute here.

[ejeschke]

No problem. Most users will not notice or need unless they have both astropy and fitsio installed.

[pllim]

Hmm where did the ReadTheDocs check go?

[pllim]

I think RTD isn't pick up the YAML file because now the default pattern they look for is .yaml and not .yml. I think I fixed it on the admin panel but closing/reopening here to be sure.

[pllim]

Oh, I misunderstood the instruction. I think we actually have to rename the YAML file. (#1078)

[pllim]

What is the behavior for files not recognized by MIME, like ASDF?

[pllim]

This seems counter-intuitive to me. Generally speaking, I thought highest priority means it would come first?

It sounds like you are using ascending order number, which is kind of like reverse of the priority?

[ejeschke]

Well, it depends on how you interpret a priority number. There are systems for where a lower number has higher priority (e.g. Unix process priorities). And it does match the typical English usage, to wit: "my first priority is ...; my second priority is ...".

I think as long as the documentation is clear on this (see conspicuous note in plugin docstring) there should be no misunderstanding.

[pllim]

Would be nice to give an example exactly what the filename should be in $HOME/.ginga and some example content of that file.

[ejeschke]

What is the behavior for files not recognized by MIME, like ASDF?

There is a set of known types that will be recognized if they are failed to be identified by ASDF. The file extension ".asdf" is one of them. But we also have a special check for ASDF embedded in FITS (especially for STScI)

[pllim]

LGTM in principle. FFTM. Thanks!

[ejeschke]

Thanks, @pllim!