Invenio-requests

- requests: add request event notification builder,
template and recipient filter

- requests: add notification flag to the service

- ui: improve styling in request items

- transifex: update configs
- ui: fix username not appearing
- requests-ui: add rendering of new entity for external emails
- links: add customization of context vars when generating them

- Update translations
- Bump invenio-users-resources

- ui: add icons for deleted communities
- requests resolvers: add system creator