Improve "content/worker" documentation:
- added more links to the Worker object;
- added details on handling the 'detach' event.
Fix issues found during the review.
Merge pull request #992 from nickolay/worker-docs

Improve "content/worker" documentation
Bug 870636, fix util/array unique
Merge pull request #993 from jsantell/fix-unique-array

Bug 870636, fix util/array unique, r+=@ZER0
Bug 834942, deprecate tab favicon getter, repurpose getFavicon
Merge pull request #982 from jsantell/tabs-favicon

Fix Bug 834942: Generalize getFavicon async method, deprecate tab favicon getter