libgui/GuiWindow.py:{onEnterWindow,__init__}(): bind wx.EVT_ENTER_WINDOW.
libroar/RoarCanvasWindow.py:applyTool(): only call tool.onMouseEvent() if mouse has moved to another cell since the last dirtying call & update lastDirtyCell.
libroar/RoarCanvasWindow.py:{onEnterWindow,onLeaveWindow,__init__}(): reset lastDirtyCell.
libroar/RoarCanvasWindow.py:__init__():
assets/text/TODO: updated.