Proof of concept: backup & restore module [DNM]

Hello,

Hopefully I'm not being to annoying putting in all these random pull requests. 

Had a play with creating a 1 click backup & restore module for RES (as described in https://github.com/honestbleeps/Reddit-Enhancement-Suite/issues/300 ). Currently its a bit rough around the edges + I've yet to fully put it through its paces in terms of cross browser testing, but i thought i may as well put in a pull for visibility even if its decided eventually not to include the functionality (due to cross browser issues/support headaches it could cause).

It utilities- the data URI's for downloading the file (just stringified JSON) + the filereader API to read the file back in. Everything appears to be working in chrome.