added method to get both unblurred and blurred snapshots in an array

@smbarne I was wanting to get both a snapshot and blurred snapshot of a view without having to get a context or call drawViewHierarchyInRect twice in a row. In my case, this involves wanting to create a blur fade-in effect for a mapview where I can also hide the mapview once it has been snapshotted. 
You can pass `0.0f` here and this function will pick the right scale. No need to get it manually.