Merge pull request #192 from cs2103aug2014-w13-1c/jin/gui

GUI redesign
Merge pull request #193 from cs2103aug2014-w13-1c/jin/gui

Use one color for cells + untick icon
Merge pull request #194 from cs2103aug2014-w13-1c/jin/gui

New settings (notifications and random colors)
Added undo and redo buttons. Closes #196