Global group is now stored and returned when using empty group

Closes dandelion/issues#139
Added empty constructor required by Spring

Linked with dandelion/issues#4
Fixed typo in comment
Improved logging during configuration loading

* Added unit tests for StandardConfigurationLoader
* Take into account the i18n.locale.resolver during the group resolution
* Removed dead code/files
* Linked with dandelion/issues#113