webwork3 client-side api & store to do list

[pstaabp]

This is a todo list for client-side api and store (non-UI) items:

• handle api errors (any non-200) in boot/axios.ts
• update components that use store fetches to handle exceptions
• switch tests to use instructors instead of admin to detect permission errors.
• test that student access to stores is handled correctly via permissions.
• [PS] switch vue names to multi-word (current version of eslint-vue won't allow single word).
• [PS] move the login code to the session store. This will consolidate a lot of code.