Add content script support to remoteEventEmitter
Add content script support to remoteEventEmitter

- before this, the remoteEventEmitter only works to/from BG script to non-content-script extension pages
- works only as a "broadcast to all"-type mode now, as that's all we need now
- in the future could be more flexible to allow specific tab IDs

WorldBrain/WebMemex,WorldBrain/WebMemex