Remove dynamic build file support.

While sometimes useful it also adds a pile of complexity to the plugin
and I think it is of very questionable value. Having assets in an ini
file makes it much easier to reason about what assets are available in
an application/plugin. Having centralized configuration also makes other
tooling simpler.
Update README to be accurate.
Add missing test.

Add a test for building files with the dispatcher filter.
Remove build prefixes and fix conventions.

* Remove js_ and css_ prefixes in build targets. They were redundant when
  you used extensions.
* Update conventions in code to not use _Foo style properties for
  objects.