Invenio-groups

- Adds space between icons and text within buttons. This follows the
bootstrap design guidelines and makes it more consistent with the
rest of Invenio.
- Reintegrates permission checks after module rewrite. (17) (19)

- Adds missing `invenio_upgrader` dependency and amends past upgrade
recipes following its separation into standalone package.

- Removes dependency on Invenio legacy package.

- Initial public release.