Paste style should paste CSS class

Summary:

I've recently transitioned to making extensive use of CSS to define styles. Unfortunately, Inkscape does not do a good job of making this easy. Besides lacking a ready way to edit the styles of multiple objects (see also #4249), Inkscape has an annoying habit of setting style on objects that should be getting their style entirely from class.

In particular, there ought to be at least an option for "paste style" to copy the class and style attributes as-is rather than setting style based on the computed style. (Admittedly, this can break down somewhat if the source object's style is partly derived from either its node type or its lineage. On the other hand, it may be desired that "paste style" results in a style that is not actually identical.)

Steps to reproduce:

• Open an SVG with some objects styled by CSS.
• Copy an object (ctrl-C).
• "Paste Style" (ctrl-shift-V) onto another object.

What happened?

The other object's style is set according to the computed style of the source object.

What should have happened?

The other object should get class and style exactly as set on the source object.