Added privacy and security section.

Bug 22354: Added privacy and security section.</li>
Bug 25784: "on air" indication is underspecified -
separated "access granted" and "on air" indicators.</li>
resolved merge conflicts
Merge branch 'alvestrand-privacy-getusermedia'
Merge branch 'master' of github.com:fluffy/webrtc-w3c
clean up change log merrge problem