[sugar] Roadmap updates

[Marco Pesenti Gritti]

* I dropped the hard code freeze for this release. With the current
speed of development of the OLPC release it would just be impractical.
I added a couple of days of delay between tarballs due and 0.82
instead, the release team will ensure some testing is made and blocker
fixes are landed during this period.

* I started a temptative 0.84 schedule:

http://sugarlabs.org/go/ReleaseTeam/Roadmap/0.84

Marco