Define BASE_URL and DATA_URL js variables in the login template. Closes #13385185 Those are expected to be defined in almost every js files. They were not before this patch because login form doesn't use the regular main template.

# re-read ComputedRelation permissions from schema.py now that we're
# able to serialize them
for computedrtype in schema.iter_computed_relations():
    sync_schema_props_perms(computedrtype.type)