Tags flairs

[olorin99]

Adds support for Piefed post flairs and user flairs/tags.

Adds user tags.

• Multiple tags can be assigned to each user.
• Tags can be created and destroyed from tags screen in settings
• Tags can be added or removed from a user via the user menu.

[jwr1]

After looking through the app a bit more with this, I have a few recommendations to make:

• I don't think there should be separate options for foreground and background colors as it just unnecessarily complicates the tag creation. I think we should just allow configuration of the background color, and then when the tag is actually rendered, calculate a good foreground color (white, or black, or maybe an off tone variant of the bg). This is exactly what GitHub does with its labels, and I think it's a good approach.
• On the screen where you can add tags to a user, there are buttons for "Add existing tag" and "Add new tag". If you click on the "Add existing tag" button, there is now another button for "Add new tag", which is a bit redundant. Maybe on the first screen there could be just one button "Add tag", and if you click on that, there would be a "New tag" button alongside existing tags.
• I'm a bit unsure of the usefulness of having the additional "Tags" section in Settings. It provides exactly the same functionality as the Tags page while visiting users, including creating, editing, and deleting tags. If it provided additional functionality (such as seeing a list of tagged users), then I could see its usefulness. At the moment, though, I'm not really sure we need it.
• It seems like it would be useful to display user tags right at the top of a user's profile page.

[olorin99]

• I changed it so the text colour is calculated using ColorScheme. I also tried using _textColor = c.computeLuminance() < 0.5 ? Colors.white : Colors.black, which I think makes the text a little easier to read but is kind of boring just having the text be black or white so I think the dynamic colorscheme is the way to go with that.

• Rearranged the add tags buttons so they're at the top of the screen. Should mean users don't have to scroll through all the tags when adding a new one. Also removed that redundant button.

• Also added a page in the settings to show all the tagged users as well as a button to clear tags for each of them.

[jwr1]

I'll go ahead and merge this, but I do have a few changes I want to personally make. I'll do it in a separate pr though so you can review them.