avoid displaying group name in the gallery

[plegall]

Since 814f430 the group name is now displayed as prefix on gallery side. Users don't really like that. We need to find a way to hide this prefix on gallery side BUT still be able to edit it on the administration (tag manager)

[ungodlyangel]

Having the same issue

[JD4x4]

Same issue and request for a fix. Thanks!

[plegall]

Note for myself: with Piwigo/Piwigo#2073 fixed, it should now be possible to edit the raw version of the tag name. Thus possible to remove the prefix on the rendered name of the tag.