add organisation and branding models

a service now has branding and organisation_id columns, and two new
tables have been aded to reflect these:
* branding is a static types table referring to how a service wants
  their emails to be branded:
    * 'govuk' for GOV UK branding (default)
    * 'org' for organisational branding only
    * 'both' for co-branded output with both
* organisation is a table defining an organisation's branding. this
  contains three entries, all of which are nullable
    * colour - a hex code for a coloured bar on the logo's left
    * logo - relative path for that org's logo image
    * name - the name to display on the right of the logo

migrations/versions/0046_organisations_and_branding.py

@@ -33,6 +33,7 @@ def upgrade():
     op.add_column('services_history', sa.Column('organisation_id', postgresql.UUID(as_uuid=True)))
 
     op.execute("INSERT INTO branding_type VALUES ('govuk'), ('org'), ('both')")
+
     # insert UKVI data as initial test data. hex and crest pulled from alphagov/whitehall
     op.execute("""INSERT INTO organisation VALUES (
         '9d25d02d-2915-4e98-874b-974e123e8536',