Create Hypothesis browser extensions for Firefox, Safari, Edge

[mkdir-washington-edu]

Related issues:

• Safari extension vision#144
• Implement Firefox Hypothesis extension #637
• Publish Firefox extension on addons.mozilla.org browser-extension#310
• Submit browser extension to Microsoft Partner Center #1119
• Publish your extension to Microsoft Edge Addons website browser-extension#552

The goal

To increase the usability of our web app, we want to see other major browsers get the same functionality and success that we've seen with the Chrome extension. We want extensions in Firefox, Safari, and Edge matching the functionality we offer in our Chrome extension.

Currently users who are not using a Chromium browser use our Bookmarklet. Edge users can use Chromium extensions, but we have no presence in the Edge web store.

[mkdir-washington-edu]

Break this up into issues for Safari, FF, Edge