Feature: Commissions

Purchases

1. Artist sets prices on types of images they are willing to draw
   1. For example, artist says it's $40 for a sketch, $80 for an inked drawing, and $160 for a colored/shaded drawing
   2. Artist can also set a limit on the number of drawings they'll accept in a given month, using one baseline value. So the artist from before might be able to do 40 sketches a month, but only 10 colored/shaded drawings. So he can say that one colored/shaded drawing is worth 4 sketches, then set the baseline value as 40 sketches.
      1. Anthony is crying thinking of how to properly implement this in a DB
      2. Nevermind he has an idea
   3. Arist can specify complexities as well--something like "each additional person in drawing doubles cost"
      1. Users select how complex something is while creating the purchase
      2. Artists can also specify work values based on complexity, so a sketch with 2 people can count as two sketches.
2. User makes a purchase
   1. User can create multiple tag_groups on the commission
   2. User also gets a description box to write arbitrary text
   3. User is charged immediately
3. Arist accepts the commission
   1. User spends