Working towards making qtlcharts available within R Markdown.

  - need to transmit chartdivid to chart

  - is there a problem if I include D3, etc multiple times?
    (need an additional argument to avoid this)
ToDo: things to do re making charts available within R Markdown
iplotPXG: chartdivid passed to coffeescript code within chartOpts
iplotScanone.R: fix typo
Add function print_qtlchart_resources, for use within R Markdown
Pass chartdivid to charts' JS code
Small change to ToDo
For R Markdown, print resources only with print_qtlchart_resources
use chartdivid in names of objects passed to javascript, to avoid duplicate names