Added mouse<->tile conversion for all map types

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2014-09-24 : v0.8.3
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* Added: Map:convertScreenToTile() and Map:convertTileToScreen()
* Added: Map:convertScreenToIsometricTile() and
Map:convertIsometricTileToScreen()
* Added: Map:convertScreenToStaggeredTile() and
Map:convertStaggeredTileToScreen()
* Fixed: Map:removeLayer() now works properly
* Changed: Tile Objects now use the tile's collision map by default