Schema handling for non-CWRC-Writer documents

[ilovan]

Problem occurred when trying to test an EpiDoc document (ISicily)

Steps to Reproduce (for bugs)

1. a. Loaded a new document from user JonPrag (Jonathan) (iSicily/inscriptions)
   or
   b. Uploaded an inscription file that Jonathan sent
   or
   c. Pasted an EpiDoc xml into the text box
2. Validated the resulting file
   Result: The file validates against the CWRC Tei schema instead of the schema declared in the opened/uploaded/pasted file (Epidoc)
3. Went to settings to check schema association
   Result: The schema dropdown shows "CWRC TEI lite" as the schema
4. Clicked on "Add new schema" and inputed the label and URL for the EpiDoc schema; hit "Add"
   Result: EpiDoc Schema is added to the dropdown list
5. Selected the schema from the schema dropdown and hit "Apply"
   Result:
   
   Also, the document would not save anymore (hitting on save doesn't do anything anymore
6. Go back to "load document"
7. Selected another inscription from Jonathan's repository
8. Hit "Validate"
   Result: File validates against the right schema.
   Check of schema in the settings schema dropdown shows EpiDoc as the selected schema.
9. Go back to "load document" and randomly load another document that is not an inscription
10. Go back to "load document" and load another inscription from JonPrag/ISicily /inscriptions
    Result: Document loads, but
    
11. Hit "Validate"
    Result: File validates against the right schema, which is also selected in the settings schema dropdown

Expected Behaviour

Ideally, upon loading a document associated with an "external" schema, the user shouldn't have to add it to settings dropdown (this should be done automatically by CWRC Writer and the validation should be run against the schema declared in the document, not against the CWRC TEI lite schema

[ajmacdonald]

The error loading schema message is because we're trying to load an HTTP resource from a HTTPS origin. We need some sort of proxy to get around that.

[ajmacdonald]

Saving gets broken because it's looking for non-existent mappings. I'll need to look into that further.

[ajmacdonald]

Even if the schema were located at an HTTPS URL, we'd still get a CORS error. So, we need a proxy in any case. I'm fairly certain this issue has been raised before.

[ajmacdonald]

cwrc/CWRC-WriterBase@73cb769

[ajmacdonald]

Related commit. Handling for entity buttons in non-cwrc-writer documents:
cwrc/CWRC-WriterBase@fa4949d