By default each user should be able to read and update the own user
branch. Also the user should be able to approve and submit changes for
the own user branch. Assign default permissions for this when a site
is created. Also add a schema migration that removes the old exclusive
read protection from the user branches and adds these default
permissions instead.
Change-Id: I961d6a191dfd4c331d2222d97f4ab9fee011f728
Signed-off-by: Edwin Kempin <ekempin@google.com>