common: Change license of some modules to LGPLv3+/GPLv2+.

* common/status.c: Change from GPLv3 to LGPLv3+/GPLv2+.
* common/status.h: Ditto.
* common/yesno.c: Ditto.
* common/common-defs.h: Ditto.
* common/gettime.h: Ditto.
* common/keyserver.h: Ditto.

This is shared code and trivial enough to allow use under GPLv2+ so to
allow use by GPLv2only software. Some of the headers are simply
adjusted to the license of their implementation.

• Signed-off-by: Werner Koch <wk@gnupg.org>