* Move AddressBar.rst into a new browser/components/urlbar/docs directory
* Break it up into several files, which makes the patch look way bigger than it really is because I used `hg cp` to preserve blame
* Add an Experiments & Extensions file/subsection, to be written later
* Rewrite the intro a little for wording and also to reflect the fact that quantumbar has shipped, and also tweak the wording of some subsection titles

Differential Revision: https://phabricator.services.mozilla.com/D38938

--HG--
rename : browser/docs/AddressBar.rst => browser/components/urlbar/docs/contact.rst
rename : browser/docs/AddressBar.rst => browser/components/urlbar/docs/debugging.rst
rename : browser/docs/AddressBar.rst => browser/components/urlbar/docs/overview.rst
rename : browser/docs/AddressBar.rst => browser/components/urlbar/docs/telemetry.rst
rename : browser/docs/AddressBar.rst => browser/components/urlbar/docs/utilities.rst
extra : moz-landing-system : lando