Internal Redesign:

- Combined MPExpression and MPMutableExpression
- Abstracted children of MPExpression into MPExpressionElement protocol
- Abstracted most of MPExpressionLayout and MPFunctionLayout into common superclass MPLayout

MathPad/MPExpressionView.h

@@ -21,7 +21,6 @@
 #pragma mark Properties
 
 @property (readonly, nonatomic, strong) MPExpressionStorage *expressionStorage;
-- (MPExpressionLayout *)expressionLayout; // Convenience Method
 
 @property (nonatomic, getter = isEditable) BOOL editable;
 @property (nonatomic, strong) MPRangePath *selection;