OO-800: upgrade http client to the new 4.x serie, fix unit tests, remove deprecated multipart entity

FXOLAT-208,OO-425: fixed changed location of tree-node-loading class and changed return value open method within FunctionalCourseUtil. Implemented some utility methods.

non-jira, OO-348: Updated tests to use instantiated site utility classes from FunctionalUtil. Fixed unsafe method clickRadio in FunctionalUtil.java.  Implementing checkCreateSubcategory test therefore I have written createCatalogSelector and createCatalogSubcategory method.

created FunctionalLocatorPairsFactory.

renamed FunctionalResourcesSite to FunctionalRepositorySiteUtil and therein renamed some fields and methods, too.
Began to implement FunctionalArtefactTest.
Some Bugfixes.

The work on FunctionalResumeTest hasn't finished, yet.