BibFormat: new configuration for I18N caching

• Replaced CFG_BIBFORMAT_ENABLE_I18N_BRIEF_FORMAT (bibformat_config.py) with CFG_BIBFORMAT_DISABLE_I18N_FOR_CACHED_FORMATS (invenio.conf) to give admins increased control over which output formats are formatted on the fly (or not) for records viewed in languages different than CFG_SITE_LANG.