Native MathML: add workarounds for mi, mo (lspace/rspace), mmultiscripts and mspace (width) elements in WebKit. Fix issue #482.
WebKit NativeMML: only apply lspace/rspace in non-embellised mrow and set them to 0 otherwise.
Address review comments.
Merge pull request #527 from fred-wang/issue482

This resolves issue #482.