patch for perspective and envelope

fixed perspective to take transformation into account #226 (closed), fixed perspective and envelope to work again on groups #218 (closed) and #155 (closed), fixed order of transformations in composed_transform (similar to merge !176 (merged))

I tested it on all the example files in the respective issues, seems to work correctly now and results are consistent with 0.92.5

The attached example has a multi-level group with lots of transforms (also showing the issue with composed_transform)