[GSOCTC-2] Command Pattern for Changing Formulas

This is the 2nd task assigned to me in GSoC 2014.  In this branch, I tried to decouple BricksList from the FormularEditor such that FormularEditor cannot directly change the formulas of the bricks. Once the formulas in the selected brick is modified, FormulaEditor will call an interface method so that the changes can be tracked to implement time capsule feature while committing the change.