[LV2] Qt5 plugin UIs and libsuil

[David Robillard]

I've pushed an attempt at sorting out these issues to suil (and
corresponding commits to jalv and ingen):

http://git.drobilla.net/cgit.cgi/suil.git/commit/?id=43a25ed63a9144afe3
2a4fea520412770394822c

Similar to Stefan's preliminary init work, but with a suil_init that
takes argc, argv, and an extensible key/value arguments in case we need
to pass more stuff here in the future.

Alas, the suil API was not designed with a global library state object
(shame on me), so argc, argv, and whatever else gets added here is
global data in the library.  I don't think this is a problem, though...
(?)

-- 
dr