Revert "remove unused GSL components"

This reverts commit 42443573.
Fixes GAUDI-1167.
See merge request !98

Conflicts:

	GaudiExamples/src/GSLTools/EqSolverIAlg.h
	GaudiExamples/src/GSLTools/EqSolverPAlg.h
	GaudiExamples/src/GSLTools/FuncMinimumGenAlg.h
	GaudiExamples/src/GSLTools/FuncMinimumIAlg.h
	GaudiExamples/src/GSLTools/FuncMinimumPAlg.h
	GaudiGSL/GaudiGSL/GaudiGSL.h
	GaudiGSL/GaudiGSL/GslError.h
	GaudiGSL/GaudiGSL/GslErrorHandlers.h
	GaudiGSL/GaudiGSL/IFuncMinimum.h
	GaudiGSL/GaudiGSL/IGslErrorHandler.h
	GaudiGSL/GaudiGSL/IGslSvc.h
	GaudiGSL/src/Components/EqSolver.cpp
	GaudiGSL/src/Components/EqSolver.h
	GaudiGSL/src/Components/FuncMinimum.cpp
	GaudiGSL/src/Components/FuncMinimum.h
	GaudiGSL/src/Components/GslErrorCount.cpp
	GaudiGSL/src/Components/GslErrorCount.h
	GaudiGSL/src/Components/GslErrorException.cpp
	GaudiGSL/src/Components/GslErrorException.h
	GaudiGSL/src/Components/GslErrorPrint.cpp
	GaudiGSL/src/Components/GslErrorPrint.h
	GaudiGSL/src/Components/GslSvc.cpp
	GaudiGSL/src/Components/GslSvc.h
	GaudiGSL/src/Lib/GaudiGSL.cpp
	GaudiGSL/src/Lib/GslErrorHandlers.cpp