Ask user for permission

[aleventhal]

Users should be asked for permission when a web page attempts to connect to js2at.

• User should be given specifics for what the js2at api wants to do and why. This information could be bundled in localized schema description files with the same root name.
• Multiple requests should be put together in one
• Web page does not need to be informed that the user said no, but it would simply not get any requests.
• The observerAdded command would not be sent to AT until user said yes.
• Open question: should the question even be asked if there is no AT attempting to listen? Probably not.
• Chrome should remember the permissions on a per-page basis.