Rating improvements

[luludotdev]

• Adds rating based on up/downvotes on detail and partial blades
• Adds up/down votes to details blade for non-logged in requests
• Adds database migration for calculating rating (for use in queries)
• Adds Top Voted route and moves the Top X items in the navbar to a submenu

[luludotdev]

For reference, this is the rating algorithm used.

It was chosen because it satisfies two major requirements:

• Beatmaps with more reviews should have an adjusted rating that is closer to their real rating, because the more reviews we have, the more certain we are that the score they give us is correct.
• All ratings should be biased towards the average rating — 50%.