Local session management

[sohrab-]

Track the current user session in a unique LocalStorage entry and offer the list of previous sessions on page load if the user wants to resume.

• Display a non-intrusive, self-dismissing prompt to let the user know there are existing sessions to resume. The modal should only appear if the user wants to continue. Do not prevent the user from working on a fresh page by having to dismiss a modal.
• Allow users to delete or clear all the previous sessions. Otherwise, it will keep building up in the browser cache.
• User sessions should now have created and last updated timestamps.
• Give the user an option to name the session for easier resume

[sohrab-]

The sessions are now persisted across refreshes as part of #89 in sessionStorage. This solves a few of our problems.

This issue probably needs to be reworked into a save/load feature