[raster] raster2pgsql should have an option to align tiles

[pracine]

We should have the possibility to provide gridx and gridy coordinates of an arbitrary grid corner to tell the loader on which grid to align the tiles produced when using the -t option. This would allow rasters having different upperleft corner alignment to be tiled on the same grid in the same table.

Some tiles would have to be padded not only on the right and lower sides but also on the left and upper sides.

Could be -A 0.0x0.0