proposal: upvote functionality

[iuioiua]

#106 is missing upvote functionality. This can be done by having the ▲ be a button that sends a fetch request to /api/vote once clicked, where a table row will be created in a votes table. The votes table will have two columns, user_id and item_id. The rest is self-explanatory.

The status of this button will correlate to whether there is a match for both the logged-in user and the current item ID in the votes table.

The main feed should also sort by amount of votes, from most to least, and display each item's score.

[iuioiua]

Completed in #154.