snf_django: Remove Help column from filter listing

Rely on a better Description rather than the extra Help column.
astakos: Improve description of AstakosUser fields

These end up as filter descriptions in `user-list --list-filters'.
cyclades: Validate VM metadata on create/update

* Check for VM max metadata items when updating/creating a single item.
* Check the length of metadata items when updating metadata items.
astakos: Fix a unicode bug in user-add

Fix a unicode bug in snf-manage user-add when the username contained
non-ascii characters.
astakos: Add checks for quota limits

Check that total (project) quota limit is no less than member limit;
and that both limits are not negative.
pithos: Recover from DB integrity errors

In Pithos+ atomicity is forced on the container level.
Hence, write operations in the account level can produce
integrity errors.

This commit handles these cases.

In PostgreSQL, a transaction is aborted
(and all the subsequent commands are ignored)
if an integrity error occurs.

Therefore, before performing an command
that can produce an integrity error,
a new savepoint is defined inside the transaction,
and after the command execution is rollbacked or committed
according to execution status.
astakos: Move code under synnefo.astakos.*
astakos: Update references
astakos: Update outer references
cyclades: Move code under synnefo.cyclades.*
cyclades: Update references
cyclades: Update outer references
branding: Move code under synnefo.branding.*
branding: Update references
branding: Update outer references
pithos-app: Move code update synnefo.pithos.*
pithos-app: Update references
pithos-app: Update outer references
pithos-backend: Move code under synnefo.pithos.*
pithos-backend: Update references