fix graph canvas dragging in IE9 and IE10

[#46554269]

Graph refactoring includes:

- a new background layer div at z-index -1
- main graph at z-index 0
- canvas at z-index 1
- plot layer is now above canvas at z-index 2
- button layer at z-index 3

Also simplified creation of button layer and button
now scales properly with graph and Interactive.