Remove unused tileGrid.getTileSize() call.
Ensure we cannot set both origin and origins in the tilegrid
Add support for multiple tileSizes in the tilegrid.

This is needed by WMTS.
Fix tests related to createBboxParam.
Add some tests for the multiple tileSizes in tilegrid.
Fix tileSize in the canvastilelayerrenderer.
Merge pull request #258 from bbinet/tilegrid-tilesizes

Add support for multiple tileSizes in the tilegrid