testing new findgtk2
Do not build yarpview if CREATE_YARPVIEW is not defined
Some fix for YARP_USE_GTK2
Properly install CMake files

Foreach is not necessary, they can be intalled all at the same time
Add variable YARP_MODULE_DIR and use it where necessary

Also use CMAKE_CURRENT_LIST_DIR where it can be used
[Cleanup]
It's not necessary to expand variable
Use list instead of set to append YARP_MODULE_PATH to CMAKE_MODULE_PATH
Remove CMP0017 CMake policy OLD, not needed
Do not modify YARP_MODULE_PATH in YarpDescribe

Use YARP_MODULE_DIR to populate YARPConfig.cmake
Do not make YARP_MODULE_PATH a list until YARP 2.4

This avoids breaking stuff for people using the stable version
Bump YARP_VERSION_TWEAK