Resolve "Unification of CMake build between gui and core"

Closes #40 (closed)

This MR:

• fixes the in-source build, when OPENPASS_ADJUST_OUTPUT=ON (currently this does create an unnecessary /gui directory and does not copy the executable and libraries of the gui at build time)
• fixes the install-step when WITH_GUI=ON, as build and install target inside the gui are now defined via cmake/HelperMacros.cmake
• introduces a new build of a static gui library inside to reduce coupling between gui modules
• various other clean ups

Tested under Windows and Linux.

gui/application/Interfaces/openPASS/CMakeLists.txt

-# /*********************************************************************
-# * Copyright (c) 2019 Volkswagen Group of America.
-# *
-# * This program and the accompanying materials are made
-# * available under the terms of the Eclipse Public License 2.0
-# * which is available at https://www.eclipse.org/legal/epl-2.0/
-# *
-# * SPDX-License-Identifier: EPL-2.0
-# **********************************************************************/
-
-set(HEADERS
-    ${HEADERS}
-    ${CMAKE_CURRENT_LIST_DIR}/PluginInterface.h
-    ${CMAKE_CURRENT_LIST_DIR}/PluginManagerInterface.h
-    ${CMAKE_CURRENT_LIST_DIR}/RandomInterface.h
-    ${CMAKE_CURRENT_LIST_DIR}/ServiceInterface.h
-    ${CMAKE_CURRENT_LIST_DIR}/ServiceManagerInterface.h
-    ${CMAKE_CURRENT_LIST_DIR}/ioplugininterface.h)