New css loader plugin, that uses <link> tags to load plain css files.
Includes the build capabilities.

Refs #213, fixes #237.
Remove duplicate d-popup entries.
Just defining it in common/global.less for now.

Refs 5e5b322e9fd093eedd9d099cd15fa88d6b548689.
forgot to add files, refs #237
ExampleWidget sample page improvements, refs #236
Handlebars: better handling for duplicate bind variables.

For example, expressions like "Hello {{name}}.  How are you {{name}}?"
or {{this.x < 0 ? Infinity : this.x}}.

In this case, generate an if() like if("name" in props) rather than
if("name" in props || "name" in props).