minor changes on configuration constants
Assets processors learn aggregation and compression

- dandelion.aggregation.enabled=true|false to enabled the asset aggregation
- dandelion.compression.enabled=true|false to enabled the asset compression

options for JS compression with YUI compressor
- dandelion.compression.js.munge=true|false
- dandelion.compression.js.preserveSemiColons=true|false
- dandelion.compression.js.disableOptimizations=true|false

Wrappers learn to retrieve contents from assets,
Configuration learn to get a property with a default value in case of.
improvement and cleaning on javadoc