add constraint to prohibit logic_id=nil for SOs

SingleOntologies should only be allowed to have
a logic_id of NULL, if there state is not done.
Merge branch 'staging' into 484-nil_handling_for_logics
Reintegrated sign in or sign up invitation in context pane if not logged in. Fixes #389.
Merge branch 'staging' into 389-signup_invitation
Show context pane for categories controller.
do not stub parsing for git spec anymore

also remove user_id not null contraint
from logics.
Merge branch 'staging' into 484-nil_handling_for_logics
force test-db migrations on travis.
Merge branch 'augmenting228_domain_field_properties' into 529-cancan_metadata
authorize metadata sub-controllers
Merge remote-tracking branch 'origin/529-cancan_metadata' into staging
Merge remote-tracking branch 'origin/524-empty_repo_history' into staging
Merge branch 'staging' into 484-nil_handling_for_logics
Merge remote-tracking branch 'origin/389-signup_invitation' into staging
Merge remote-tracking branch 'origin/clone_url_links' into staging
Dot in sign up invitation.
Use full width, if context pane is not shown.
do not use ALTER TABLE IF EXISTS

Since we also need to support PostgreSQL 9.1,
we can't use the ALTER TABLE IF EXISTS, since
IF EXISTS on ALTER TABLE was introduced in 9.2.
adjust factories to set logic for ontology.
Merge remote-tracking branch 'origin/484-nil_handling_for_logics' into staging