[BUG] Adding Multiple Tags field to multiple selected files breaks Tag assignment

[SirPhilip3]

Steps to reproduce

1. Select two or more files
2. Add the Tags field
3. Add another Tags field
4. You can now add Tags only to the first Tags field , the second will always remain empty and the tags added to this field will be added to the first field instead

https://github.com/TagStudioDev/TagStudio/assets/118560349/b01e3cc3-2216-46df-8636-6c150a673fde

[Loran425]

This is currently a known bug, that was caused by some of the changes allowing multiselection to work. I believe the plan is to fix this with the JSON->DB swap that is in progress but for the moment limiting to a single tag group of each type (tags/content tags/meta tags) is probably the easiest way to prevent this from occurring.

A library loading bug was causing TagStudio to not recognize existing tag groups and add copies, this unintended multiple group creation should be resolved if #95 is merged but this particular issue having multiple tag groups remains.

From the UI you can remove the second tag group without issue if you decide to work with one tag group.