HtmlMesh Updates

[ericwood73]

• Fixed issues when canvas is offset or repositioned which was preventing the HtmlMesh from working in PG if the editor was open
• Add a dispose method to the renderer to allow the DOM elements and listeners as well as the scene observables to be removed when the scene is destroyed (e.g. PG is executed)
• Handle rotations about multiple axes
• Capture pointer events while dragging to allow a camera rotation that brings the pointer over the mesh to trigger capture
• Address some bugs with pointer capture causing inconsistent capturing behavior when a skybox or background is included.