Fix Issue #707 Set size of R graphics by defining a new function in the ...

...beaker module where you can give all the options to the SVG renderer (including width and height).  This introduces a complication which is you cannot access these options until they are defined, and our normal evaluation path does SVG setup, so I had to add an option to the evaluate REST call for "init" evaluations that do not do all the wrapping and output capture that normal user evaluation does