App Placeholders

Porting a proposed v2 enhancement to v1.  Here are the updates so far:
* fixed duplicate sourcemap call in Gruntfile
* added F2.loadPlaceholders
* fixed comments surrounding the CSS classes that are applied to apps
when rendering
* fixed a bug where the wrong CSS classes were being applied with the
default AppHandlers
* added logic to allow placeholder apps to bypass AppHandlers
* added autoload logic for placeholders
* added a basic container to demonstrate placeholder functionality
* added unit tests surrounding placeholders
* fixed a bug in the example containers where the proper CSS classes
were not being applied