cyclades: Fix bug in DB migration

Fix bug in migration 0102 which saves in the 'subnet_ids' column of the
network object the IDs of all subnets that are associated with this
network. A typo in this migration resulted in the 'subnet_ids' field to
contain the id of the network. Also, provide a DB migration to fix this
issue for those that have already installed 0.16rc1.
docs: Fix typo
docs: Fix bad reference
astakos: Provide smarter defaults for project_default

When registering a resource, set project_default to zero if the
resource is meant to be api-visible, otherwise to infinite.
docs: Mention project default in the admin guide

Also rephrase system default section in install guide.