Reddit compatibility

[thundergolfer]

Thought there was no reason that this extension shouldn't cover content on Reddit as well, so I worked on implementing it.

Issues

• Unlike Facebook, Reddit doesn't tell you the content-type in the HTML, so a request is made to check content-type in the headers. This content-type is passed from a background script to the content script, but at the moment the request is failing sometimes.
• Testing this PR was hampered by the fact that the herokuapp is unavailable at the moment, but the response of the herokuapp can easily by stubbed to check the functionality.

Other changes

• the verified/unverified buttons is now a span rather than a div for Reddit.
• removed unnecessary whitespace from some lines.

[thundergolfer]

@anantdgoel @HottaSho @nabanitade Any movement here? Cheers