Convertion from handle to value type classes

Handle classes proved difficult to debug in a large scale codebase. Main external changes include:

• renamed xCg to xcg
• renamed WindCustom to Wind class
• removed WindMatlab class
• removed update methods (e.g. rocket.updateCutoff). Note: wind.updateAll is still available to regenerate distribution
• converted parachute array to parachute cell array

Converting to value classes with auto-updaters allows for greater flexibility and maintainability