Add yang-common JMPS javadoc
Add yang-common JMPS javadoc

This adds Module-level documentation, at least its bare bones.

Change-Id: I08c98f111063d3dffb1f2812aab69a20de289ea5
Signed-off-by: Robert Varga <91ae5aa8c7a9f7e57b701db766e23e544aaa6ae9@pantheon.tech>

opendaylight/yangtools,opendaylight/yangtools