Massive refactoring to clean up models

* Tweak style of quantity label in output box to be more visible
* Move data files for all mods under a directory for the specific
  version of the mod
* Add a `silent` property to the base model to prevent models which
  shouldn't be observed from emitting events
* Change the term "itemSlug" to just "slug" across the board
* Change all models so that they don't require their parent in their
  constructors and so that they don't automatically add themselves to
  their parents lists
* Remove a bunch of unnecessary event triggering
* Tighten up access to various lists of children across all models
* Refactor the guts of the V2 parser into an abstract base class so
  it can be used for other parsers in the future
* Remove a number of unused methods

src/templates/crafting_table.jade

@@ -18,7 +18,6 @@
         .output
             a: img
             p.quantity
-            p.quantity
             p.multiplier
         .next
         .problem