Add brand_type to EmailBranding.

It makes more sense to put the brand_type with EmailBranding rather than in Service.
Next step is to add the new type to the form in admin app.

migrations/versions/0214_email_brand_type.py

@@ -0,0 +1,25 @@
+"""
+
+Revision ID: 0214_email_brand_type
+Revises: 0213_brand_colour_domain
+Create Date: 2018-08-23 11:48:00.800968
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = '0214_email_brand_type'
+down_revision = '0213_brand_colour_domain'
+
+
+def upgrade():
+
+    op.add_column('email_branding', sa.Column('brand_type', sa.String(length=255), nullable=True))
+    op.create_index(op.f('ix_email_branding_brand_type'), 'email_branding', ['brand_type'], unique=False)
+    op.create_foreign_key(None, 'email_branding', 'branding_type', ['brand_type'], ['name'])
+
+
+def downgrade():
+    op.drop_constraint("email_branding_brand_type_fkey", 'email_branding', type_='foreignkey')
+    op.drop_index(op.f('ix_email_branding_brand_type'), table_name='email_branding')
+    op.drop_column('email_branding', 'brand_type')