Replace all app references to [email protected] with link to the support web form

[mattdricker]

We are moving to direct support requests more and more to use our support web form at https://web.hypothes.is/get-help/ Doing this helps improve the quality of the requests by prompting for details that make the support process more efficient.

To this end, we'd like to replace instances in the app that prompt or suggest the user email [email protected] with prompts or suggestions to use the web form. These are almost exclusively in our error messages, but there may be other locations as well.

[mkdir-washington-edu]

I suggest we add email validation and explore other ways of verifying users to the form before making this change. We see somewhat frequent email typos in addresses when users type them to us.