Add release notes for Review Board 2.0.10.

This covers all the fixes and optimizations made since 2.0.9.

Reviewed at https://reviews.reviewboard.org/r/6499/
Release Review Board 2.0.10.
Merge branch 'release-2.0.x'
Bump to 2.0.11 dev.
Don't crash with invalid timezones.

If a user's browser is sending an invalid timezone string, we shouldn't prevent
them from using Review Board.

Fixes bug 3594.

Reviewed at https://reviews.reviewboard.org/r/6501/
Merge branch 'release-2.0.x'