add fallback height/width settings for JBrowse container
add fallback height/width settings for JBrowse container

nathandunn/jbrowse,GMOD/jbrowse,nathandunn/jbrowse,GMOD/jbrowse,GMOD/jbrowse,GMOD/jbrowse,nathandunn/jbrowse,GMOD/jbrowse,nathandunn/jbrowse,nathandunn/jbrowse