Added new placeholders for filtering

Linked with dandelion/issues#116
Typo in comments
Added support for sorting functions

* Added a new SortingFeature which is registered in the
TableConfiguration as soon as a column has a not blank sortType
attribute
* Linked with dandelion/issues#53
Added support for sortType attribute in AJAX

And removed unused getters from the AbstractColumnTag
Linked with dandelion/issues#53
Updated Person mock object
Fixed getConfigurationFromPage

Allowing to get the generated WebResources in tests
Removed Reflections from the dependencies

* Updated ClassUtils by adding method allowing to scan a package
* Updated ExtensionLoader and ExtensionManager
* Added ExtensionLoadingException
Refactored extension loading and exception handling

* features and plugins table attributes removed
* ExtraCustomFeaturesProcessor and ExtraCustomPluginsProcessor replaced
by ExtraCustomExtensionProcessor
* ext / dt:ext table attributes added, allowing to set a list of
extension to load (plugins, features)
* All extensions now throw a ExtensionLoadingException during the setup
method
* TableConfiguration has been simplified: it now has internalExtensions
and extraCustomExtensions as new fields. Default properties and
Configuration have been updated accordingly
* New IT for custom extension loading
* All methods of ClassUtils now throw native exceptions. All exceptions
are now wrapped inside adapted custom exception and then throwed
* The WebResourceGenetor now entirely delegates the extension
registering and loading to the ExtensionManager
* Closes dandelion/issues#108