This massively reduces the number of temporary ol.TileCoord objects.
Previously an ol.TileCoord object was generated for every potentially
visible tile at the current zoom level and lower, every frame. This
commit eliminates all of those. Now new ol.TileCoord objects are only
allocated when a new tile is created.
This change adds a lot of flexibility to working with tile
layers: Sources where the server projection or tile grid do not
matter can now be constructed without specifying a projection or
tile grid.
The tileUrlFunction/imageUrlFunction now also creates updated
URLs when the params of the layer change, so things like
mergeNewParams in ol2 will be possible.
A nice side effect of this whole change is that there is no more
duplicated code between tiled and single image WMS layers.
While I was at it, I also fixed a WMS 1.1.1 axis order issue
and incorrect STYLES params (STYLES=& instead of STYLES&).
Previously, the findInterimTiles method was returning undefined if the min x/y coord for a tile range was already in the lookup. The return says it indicates whether all tiles for the given z are loaded. This change corrects the return.
This change also reveals a misunderstanding of the tile range returned by `getTileRangeForExtentAndZ`. The previous findInterimTiles method was treating max values as inclusive. This is intuitive. It looks like the method returns a range where max values are exclusive.
