Clean up of the htdocs/themes directories.

[drgrice1]

Move gateway.scss and achievements.scss into htdocs/js subfolders. Rename the math4.js file to htdocs/js/System/system.js. Rename the math4.scss file to htdocs/js/System/system.scss. These files do not belong in the theme directories and should not be considered theme-able.

Where possible, the page specific code in the math4.js (now system.js) file has been moved into the page specific JavaScript file for that page.

The aria label hack that was in math4.js has been removed. It is clear that is not doing the correct thing, and it is probably less of a problem to have an aria label that reads "answer 1" even when there are no other answers than the numerous cases that it is changing aria labels to just "answer" when it shouldn't. One case is if there is only one text answer and there are other answers (radio buttons, checkboxes, etc) on the page. In this case the "answer 1" is changed to "answer" even when there is more than one answer on the page. Also in gateway quizzes the "problem n" prefix is removed if there is only one problem on the page, and it shouldn't be. Aria labels in general need to be rethought, but this JavaScript hack is just incorrect.

Update the README files in the themes directories a bit. More could be done here to give better directions on how to customize themes.

The name of the htdocs/js directory really needs to be changed. It is really the public "assets" location, and not just JavaScript. The htdocs/css directory should be removed as well.

Also change "npm install" to "npm ci" in the warnings that are issued if the static-assets.json files are not found.

Move the system.html.ep template out of the themes. That file is now the system layout instead. This file should really not be themable. If someone wants to mess with that file, they can deal with having locally modified files that show up as changed by git. If someone does not know what they are doing, they can really mess up things. If there is some other thing that is commonly wanted in the default system layout it can be added as an option.

So now the themes directories only have what is needed for theming, and theming for the most part is only about changing the color scheme. This is how it should be. Theming should not mean modify the entire system to make it be what you want.

There are several advantages with this pull request. It removes the need for so many symlinks from the math4 theme variants back to files in the math4 theme. It removes the need for the hackish htdocs/themes/layouts symlink that turns the themes directory into a layout directory. It removes the need for the themes directory to be a template path to begin with. The template files should not be in a publicly accessible location in any case.

[pstaabp]

Looks good. I have a couple of customized themes and did remove the system.html.ep files from those directories.

Also added a label to update the wiki. I don't think the wiki will need much changes, but we should review that.

[drgrice1]

With this pull request if you still have the old files (or links to them) in the themes directory for a customized theme, it won't matter. The files won't be looked for in those locations anymore. Most notably, this is true for the system.html.ep file. The themes directories are not template directories at all anymore.

[pstaabp]

Separate from this PR, but wondering if we should get rid of the 'math4' language in the theme. I know there were other themes before, but I would guess any newish users don't know anything but math4.

[drgrice1]

Yeah, I also don't like the mathN naming. I didn't go to the extent of renaming it yet though.

[Alex-Jordan]

Tested by checking out the branch and playing with theme settings. Not a thorough test, but I think it is good enough.