net-im/qxmpp: Update to 1.6.0

Update LICENSE - it's really LGPL21+

Remove wonderous use of USES=libtool alongside of USES=cmake. Still
trying to figure out how that ever came to pass.

Disable building of examples which we wern't installing anyways and make
PLIST_SUB more readable.

Add a TEST option to optionally build tests (previously on by default),
which eliminates ~274 targets for normal builds, but still lets us check
if everything is all hunky dory.