Clean up service and view contributions from extensions

* Unify terminology to use `contributed_*`, and only `ggrc` has the
  `all_*` and `init_all_*` methods
* Use `ggrc.extensions.get_extension_modules` instead of using
  `settings.EXTENSIONS` directly
Fix `mapping_counts` helper when to mappings match

* E.g., no mappings are defined for Threats, etc, but the common tooltip
  should at least not fail
Update Template and RiskAssessment objects

* Add `_fulltext_attrs`
* Add `description` to Template.publish_attrs
Add templates and client-side models for RiskAssessment

* Added Threat, Vulnerability, Template models and modal_content
  templates
Fix issue with `get_extension_modules` with no extensions
Fix `ggrc_gdrive_integration` for new extension
Extend `public_config` implementation for extensions

* Basically, settings "exports" from extensions are now additive, and an
  extension-module-level method is available for providing
  permissions-dependent config.
* Also, add `ggrc_config` Mustache helper to make client-side config
  variables available in Mustache templates
Display "Superuser" in UI for "default admin" users

* Makes `BOOTSTRAP_ADMIN_USERS` config available to client-side, *only*
  to Admin users.
* Shows "Superuser" in top-right dropdown when applicable
* Shows "Superuser" for specified users on Admin page in Roles
Enable configuration of Risk Assessments UI URL

* `RISK_ASSESSMENT_URL` is now a config variable, and available on
  client-side for Admin users
* Use this new config variable in templates to link users to the correct
  external server
Merge remote-tracking branch 'origin/develop' into feature/add-lhn-other-risk-assessment-objects

Conflicts:
	src/ggrc/views/__init__.py
Merge pull request #946 from reciprocity/feature/add-lhn-other-risk-assessment-objects

Add other Risk Assessment-related objects to LHN