FEAT: Link Folders

[steven-tey]

The distinction between this and our tags feature is:

• Tags are many-to-many, while Folders are many-to-one (one link can only be a part of one folder
• This makes Folders a better way to organize your links from visual perspective, while tags are more of a way to categorize your links.

Bonus: You should still be able to get the stats for all links in a given folder, similar to how it works with tags.