Add the ability to create tags when adding a tag to a file

[bjorn-out]

Closes #1

• Adds a button to the "add tag" modal, below the search results, to create a new tag with the search query as its name, and immediately adds it to the file.
  • It will be a simple tag with no subtags or aliases, and a random color will be assigned.
  • If there are no search results, hitting enter will also create a tag.
• Search box is now cleared when the modal opens.

Ability to change further details for the newly created tag (like subtags) should be added. My suggestion would be to allow editing any tag in the search results by right-clicking. I tried to implement this, but did not get it to work yet.

I do believe the full tag creation modal should not pop-up by default, as this is frankly annoying when trying to tag many files manually. You can already use Ctrl + T or Cmd + T if you want to create a tag with more details, or use the aforementioned edit button once implemented.