Use localStorage to retain edited state

[chipcullen]

It would be nice if changes that were made were automatically saved to the user's localStorage, so if they come back, they can pick up where they left off.

Aspects of this issue:

• [ ] Creation of a config object that is saved on every change
• [ ] What does the config object capture? Only font settings? Any changes to the text?
• [ ] Test for the existence of a saved state on initial load
• [ ] If the user comes in via a shared URL - use that URL's settings to override the config object (update instead?) Warn user of override?
• [ ] Set / read of config object