package/davici: new package

package/davici: new package

This patch adds davici which is an alternative implementation of the
VICI client protocal used by Strongswan.  It targets better integration
with software stacks and uses a asynchronous, non-blocking API that can
be integrated in third-party main dispatching loops without the use of
threads.

Signed-off-by: Jared Bents <jared.bents@rockwellcollins.com>
[Thomas: fix license, it's LGPL-2.1+, add entry in DEVELOPERS file.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>