New Spring way to render cached web resources
Updated the AssetController, allowing to render cached web resource instead of the configured concrete implementation of the AssetServlet
The Spring dependency is now based on a range, starting from the 3.0.0.RELEASE (@ResponseBody)
Note that:
 * the controller must be configured in end-user applications using:
<import resource="classpath:dandelion.xml" />
 * No need to add the import directive in almost all Dandelion samples since the base package scanned in the Spring config is "com.github.dandelion", which is most of talready scanned