Implementation of inspection system

A mostly complete implementation of the inspection system.

See ExampleInspectable.cs for an example.
Try it in-game by clicking on the sphere added for testing.

Features:

• Different types of properties (string, int, float atm, easily extendable for any type implementing IFormattable and IConvertible)
• Properties can be editable (if isEditable is set to true).
  In this case, a they will be displayed differently in-game, with appropriate restrictions on the entered value. (eg.: only digits for integers)
• Any change in property values is reflected in the view.
• Commands put buttons on the inspector panel. They can have any number of object arguments and return an object.
  Although this circumvents the type system, a method signature can be provided for run-time type checking.
• A Command might not be available at any moment, this is implemented with the CanExecute property.

Notes:

• I choose objects for commands in order to significantly reduce code repetition. I don't think generics could help because of commands with different number of arguments.
• There are some TODO: change sg. to internal comments in the code.
  I left those in because otherwise the example wouldn't compile.
  We can change those access specifiers to internal in a future refactoring once the system is in place and working.