Add an indicator when a tag you're about to add is already present on the edited selection

[mieldepoche]

When tagging a picture with lots of tags already, it can be hard to detect if the tag I think of is already present or not in the list, which sometimes leads to accidentally removing tags and having to add them back.

To fix this, what about differentiating the already present tags by giving them a special character in the tag search thingy? The symbol could even be different depending on wether the whole selection already has the tag, or only a subset of it.

current/unused tag	tag present on subset of selection	tag present on whole selection

alternatively instead of displaying a symbol, there could be the selection usage shown next to used tags:

current/unused tag	tag present on subset of selection	tag present on whole selection

That way, you can see at a glance if the tag is already present.