Manage a null or empty location case
Provide the possibility to have multiple properties files as configuration

The default properties file remain 'dandelion/dandelion.properties'
But now you can setup more configuration in files like 'dandelion/dandelion*.properties'
little refactor on wrapper + javadoc
Add configuration for webjars assets location wrapper
Manage 'default' properties in 'dandelion/dandelion.properties'
Provide the ability to setup multiples sources of assets loaders

In 'dandelion/dandelion.properties', 'assetsLoader' become 'assetsLoaders'.
'assetsLoaders' is a list of 'AssetsLoader' separated by comma