remove old export functionality, move new in place
add cmake option FIND_SHARED_LIBS

Defaults to ${BUILD_SHARED_LIBS} and lets the user decide if
static or shared versions of third-party libraries are
searched.

Only applied to HDF5 for now.
fix link bug for static builds
actually include target info in export config
move export functionality towards the end of CMakeLists.txt

This ensure that all referenced variables are actually defined.
Merge branch 'nschloe-export-fixes'