Make the themes/load! plugin accept any path.
Previously it required the CSS to be in the dui/themes directory.

Refs #14 sort-of.
simplified
Require paths to load! to contain {{theme}} substitution variable.
Remove RTL handling code from load!, punting the job to the widgets.

A widget that with both LTR and RTL CSS will have a define() dependency list including text like:

	"./themes/load!./themes/{{theme}}/StarRating",
	"dojo/has!dojo-bidi?./themes/load!./themes/{{theme}}/StarRating_rtl"