REFAC: Exposes axes length of renderer in the VTKViewer

This exposes the axes length in the VTKViewer. Previously users would have to do:

std::dynamic_pointer_cast<VTKRenderer>(viewer->getActiveRenderer())->setAxesLength(x,y,z);

now they can just directly do:

viewer->setAxesLength(x,y,z);

I believe it's more appropriate the viewer has this.

PR Checklist

• No API changes were made (or the changes have been approved)
• No major design changes were made (or the changes have been approved)
• No new dependecies were added (or the new dependencies have been approved)
• Added test (or behavior not changed)
• Updated API documentation (or API not changed)
• Ran the CodeFormatEnforcer task and verified the header is in all new files
• Added iMSTK examples for all new major features (if any)