Remove blue border from textbox when focused

resolved #82
Changed X button image

Resolved #80
Fit groupLabel to mainVBox
Removed borders around window

Yay!
Implement command history

Resolves #86
Show category
Hide scrollbar buttons and removed the border

The up-button is covered by exit button so it is hidden.
resolve #79
Added app title bar

Resolves #87
show hints
Added hintLabel
Fixed hints not working after space
Changed scrollbar design

Resolves #79
Changes in showing hints
Change in ToDoContainer
More changes in hints

fixes showing hints for key changes when mainInput is not focused
Merge pull request #97 from cs2103aug2014-t17-3j/UI-updates-for-V0.3

Ui updates for v0.3