Fix blocked_redirect by fixing promises and images

[IAmThePan]

Duplicate of PR #379 but off the Hotfix branch:

Fix Blocked Redirect:

• Fix images from not showing. I did this with as little change to the code as possible. The solution was to just add PNG files to the extension.
• Fix promises and sendMessageInPromise to return correctly. There was an extra set of () that prevented sendMessageInPromise from returning correctly. There was also no return in content-scripts/utils/msg's sendMessageInPromise which prevented the function from correctly returning a promise.

@christophertino Please approve.

[christophertino]

This fixes #376