Handle transform attribute

[sprocketc]

This is probably going to be the trickiest element attribute.
We need to automatically update it in order to rotate our elements, but we also need to allow manual editing in order to remain consistent with one of the main goals of this project.

Changing this attribute would also affect the bounds of the element and the behavior of the element when we translate or scale it.

We need to parse its value and and apply any transformations to the parsed attributes.
Converting the existing transformation to a matrix might be a good idea in order to apply our transformation to it, but we will the have to switch back to the other transform functions (translate, scale, rotate) if we want to maintain its readability.

MDN docs