Added fundation for new Thymeleaf testing lib
Refactored code and added comments

Linked with dandelion/issues#113
SystemConstants is now used everywhere
Updated configuration loading mechanism

* cssClass, cssStyle and labels are now processed using the new
configuration loading mechanism
* labels renamed to extraLabels and default properties file updated
accordingly
Fixed initialization of default configuration

Linked with dandelion/issues#113
Updated configuration loading mechanism

* DatatablesConfigurator is not a buggy singleton anymore
* cssClass and cssStyle are now working when using properties file
* Fixed exportLink initialization when cloning an instance of
TableConfiguration
* featureAppear renamed to extraAppear
* Added comments
* Removed dead code
* Unit tests updated accordingly
Updated configuration loading mechanism

* Added a new StringBuilderProcessor for cssClass and cssStyle
attributes
* Renamed some private field in JSP unit tests