Incorporated Wayne's suggested changes

- Up to 2 F2F meeting per year (was 1) are now possible on top of F2F at TPAC
- Presentation API description updated, using same wording as in scope section
- Added @@ next to the link to the CG report. Also clarified that the report
is a final report. This needs to be updated before the AC review, either with
the link to the final report if it is published or with an explanation that the
CG is about to finalize the report otherwise
- Dropped mention of Last Call for the test suite as that step is likely to
disappear in a near future
- Updated expectations re. CG focus after WG creation and clarified the need
for a Dual License accordingly
- Clarified the overlap with the NSD API and the expected outcome of the
liaison with the Device APIs WG.

See Wayne's feedback and discussion at:
http://lists.w3.org/Archives/Public/public-webscreens/2014Jun/0028.html
Added explicit liaison with Second Screen Presentation CG

Also dropped sentence that said "The Working Group and Community Group will
never work on the same deliverable" since that cannot be guaranteed in
practice.
Merge pull request #9 from tidoust/wayne

Incorporated Wayne's suggested changes