Updated charter to address W3M requested changes

The draft charter was reviewed by W3C Management. The following changes
were made as a result:

1. The following text was added to the Scope to clarify support for more
than one secondary display to address accessibility requirements:
[[
  Sending content to a connected display creates a presentation session.
Applications can create multiple presentation sessions to control
multiple displays, although synchronization between them is not
currently supported by the API.
]]
2. the license was reverted to the usual W3C Document License. The dual
license remains an experiment in the HTML WG for the time being.

Other updates:
- chair and staff contact names added
- URL of the Presentation API CG final report updated

Note the draft charter has been copied to W3C space per process and is
now also available at:
http://www.w3.org/2014/secondscreen/charter-draft.html