Invenio-accounts

- alembic: adapt recipe to mysql

- alembic: fix upgrade recipes

- models: add managed field to groups
- models: alter primary key type of group (id)
- cli: pass id on create role action

- models: add support for locale in user preferences

- global: replace deprecated babelex imports
- update invenio-i18n

- cli: add `--confirm` flag when creating a user
- new config variables to set the default user and email visibility
- register_user: method accepts new argument, `send_register_msg`, to control
programmatically the send of registration email independently of the global
configuration.