Move ClassLoaderUtils

This patch makes an attempt at unifying and improving the two
ClassLoaderUtils versions we have available. This is a prerequisite to
being able to being able to maintain them properly.

At this point the sanest place for them is yang-binding, as it has
guava, slf4j and is at least transitively pulled from all users.

Change-Id: Iea7ae5fb7ef40f9af960ca01b000f81237c70ab0
Signed-off-by: Robert Varga <rovarga@cisco.com>