Add Undo/Redo to InputTextWidget
Disable Actions if they can't used (i.e. nothing to copy)
Don't allow to copy an empty sting
Add placeholder to InputTextWidget
Add missing Undo/Redo icons.
Add FIXME commtents to replace the placeholder implemetation of InputTextWidget by Qt 5.2s own placeholder.
Reformat some code (brackets).
Merge pull request #48 from Schlumpf/input-text-widget-undo

Add Undo/Redo to InputTextWidget