Fix html layout issues.

Previousely there was a concern that all plots will be placed into
separate iframe. But in this case it's easy to adjust iframe size
automatically (no scrollbars should be displayed). So now we draw
all placeholder divs at server side using jelly ML and use iframe
only to isolate our jquery scripts from Hudson javascript libraries.
Consider 'null' value for numberOfBuildsToUse parameter as a hint to include all builds.