Invenio-admin

- remove deprecated flask_babelex imports
- install invenio_i18n as explicit dependency

- Replaces pkg_resources with importlib.

- Fix *long* standing issue with newer flask-talisman having changed its interface.

- Adds theme dependent icons to the settings menu.

- This release was available on PyPI for about 1 hour, but was removed because
it was breaking compatibility. Instead v1.3 was released.

- Minimum version of Invenio-Accounts bumped to v1.1.4 due WTForms moving the
email validation to an optional dependency.
- Minimum version of Flask-Admin bumped to v1.5.6 due to a fixed SQLAlchemy
1.3.6 compatibility issue