front: Consolidate native lib loading to CoreInterfaceNative.

Consolidate loading the ae-bridge/sdl/core/front-end libraries to one
place.  Simplifies maintenance.  Putting it in CoreInterfaceNative is
also a better place because it guarantees that those 4 libraries will
always be loaded before any other calls to the native methods.

Also, moving the lib loading functions to CoreInterfaceNative from
FileUtil ensures that those 4 libraries will always be loaded before
any of the plugins.