GUI: handle tags in NameDescTagsWidget

[tangkong]

Current Behavior

Currently, if you try to add a tag, the app will crash.

Expected Behavior

We should be able to add tags

Context / environment

This requires us to actually implement tags on the client side as well. A few things need to be done specifically on the GUI side:

• Adjust TagsWidget to expect the dataclass field to be a set, not a list. This is easy enough to do, updates will probably have to just re-create the set every time the tags are updated
• Ensure these tags match the permitted Tag class members (these are Flags), and make sure they serialize correctly

unearthed in #90

Steps to Reproduce (for bugs)

1. Open a Page (collection builder page, for example)
2. Click the "+" button to add a tag
3. 💥

Suggested Solution

See context