Complete data scheme overhaul

 - individual tags instead of concatenated ones for each picture
 - Tags are associated to the tagging user.
 - Votes are associated to the voting user.
 - Comments can be voted up or down.
 - Images, comments, and tags can be marked deleted with a reason.
 - Prepare for password hashs produced by password_hash().
 - Store access tokens and image hashs as binary strings.
 - Store timestamps as BIGINT because other possibilities of MySQL
   and MariaDB suck or offer no real advantage over BIGINT.
 - Legacy user score and image ratings can be retained.
 - Lots of views do demonstrate and/or facilitate access to aggregated
   data
 - Abuse notification managment for things like spam, porn, copyright
   violations, or generally unethical or illegal content

I also included a crude migration script for old data as seen on Lowbird.