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. 
If you want, you can use the abbreviated ternary syntax. This line is equivalent to the shorter and potentially less error-prone:

```
id unblurredImageOrNull = unblurredImage ?: [NSNull null];`
```