Update user_collection meta information on transformative updates

[jrconlin]

Blocks on #789

After an operation that potentially modifies the stored bso data, the meta data information should be updated after the status is returned to the client.

An example SQL function may be:

UPDATE user_collections SET count=(
  SELECT COUNT(*) FROM BSOS WHERE 
  FXA_UID="000148c5a52fda4e413625bd0287b6aec7f509f48717bc8de9f8df58308accfc" and 
  FXA_KID="31008d7c3f916aaf744dbe4121dc5d0e" 
  and collection_id=7
), total_bytes = (
  SELECT sum(byte_length(payload)) from BSOS WHERE
  FXA_UID="000148c5a52fda4e413625bd0287b6aec7f509f48717bc8de9f8df58308accfc" and 
  FXA_KID="31008d7c3f916aaf744dbe4121dc5d0e" 
  and collection_id=7 
)
where 
  FXA_UID="000148c5a52fda4e413625bd0287b6aec7f509f48717bc8de9f8df58308accfc" and 
  FXA_KID="31008d7c3f916aaf744dbe4121dc5d0e" 
  and collection_id=7

(Example is illustrative. Some optimization may be required.)