Feature/type attributes

[Mwexim]

Adds a new registration system for types to easily register additional behavior for types, like ranges, default changers, arithmetic, and more. My goal primarily was to provide addon developers with a system to easily bundle attributes together.

Additionally:

• Reworked ExprDifference and removed its quirky conversion methods. I might add a better conversion system, but probably for the type attributes themselves rather than in the expression class.
• Reworked ExprRange.
• Refactored a lot of code, and improved the registration of PropertyConditionals and PropertyExpressions.

This pull request will be completed later with some other additions:

• A conversion system to easily convert an object to a type with a specific attribute. I will see how I will implement it later.
• Container attribute for things that contain other things (except lists). Currently only strings contain other strings, but in the Bukkit implementation, inventories act as containers.
• Comparable attribute, issuing the removal of the Comparator system and moving it to the attribute system.
  After consideration, I decided that type attributes should only be for one type, and not multiple types at once, which the current comparator system supports.
• NumericalArithmetic with multiply, power, division and other math functions.
• a getZeroValue() function for the Arithmetic attribute, so it can be used to reset variables for example.