The side panel opens with the Space key, this panel can contain
widgets to assist the capture with more features.
This commit fixes the preview of the tool hiding it when the
mouse hovers a widget. This is more needed now having a new widget
inside the CaptureWidget.
More flexible tool API
Minor code format fixes
Clipboard freeze fixed(?)
Arrow correcly growing close to the start point
Improve maintainability
Add undo/redo stack