Added cell highlighting to GameBoardEditor
Storing CellOrientation in BoardGraphicsScene tiles' items
Memoizing tesselation in GameBoardEditor::ItemEventsFilter
Moved item tool overlay for hovered item to separate graphics effect.
Refactored event filtering and graphics effect in GameBoardEditor.
Removed BoardTilePixmapItem::opaqueArea

Default implementation should be enough, it doesn't need to be
re-implemented
Improved implementation of HiglightGraphicsEffect

Uses painter path instead of polygon. Still doesn't draw as expected, but
at least now there are no obvious errors in implementation.
BoardTilePixmapItem clips to shape by default.
Removed unnecessary position checking in GameBoardEditor event filter.
TileTypes::BOARD_TEXT items don't get tool overlay effect.