Enhancement to expand button in tag drawer - give authors opportunity to add tags when they expand any taxonomy

[jmakowski1123]

As an author, when I click to expand a taxonomy in the tag drawer and it has no tags added yet, I expect to be able to start adding tags. Instead, I see an empty expanded space. I would expect to see the full tag list from which I could choose to add tags, and I don't immediately see the "edit tags" button on the bottom of the drawer. When I click on the expand button, I would like to see a link that tells me I have no tags yet but can add them. "No tags added yet. Add tags +"

Clicking that "Add tags +" link would have the same effect as clicking the "Edit tags" button that's below.

[pomegranited]

@jmakowski1123 @bradenmacdonald CC @ali-hugo I chose to use "Add tags" as the button text here instead of "Add tags +", because there was already an existing button by that name (and nowhere else uses the "+" convention).

Is that ok?

[ali-hugo]

@pomegranited That makes sense to me. I'm happy with just plain "Add tags".