Bioclim should handle 0.5 degree resolution variables

[goldingn]

raster::getData can go down to 0.5 degree resolution, but this requires downloading the relevant tiles by defining a lat-long. We should be able to grab all of the tiles in which the extent falls in the extent, mosaic them and crop to the extent.

[AugustT]

@goldingn This was raised by a guy at the workshop who wanted to know why in the bioclim module he could not set resolution to 0.5, thanks for flagging