Qt 5 support

[Georg Rudoy]

Hi,

I've started adding support for Qt5 in LeechCraft codebase. I've also
took a few CMake macros from Oleg Linkin's qt5 branch to ease
supporting both versions of Qt at the same time, like FindQtLibraries,
QtWrapUi and QtAddResources. Sorry Magog, that wasn't a merge, so no
attribution in git log despite you did a great job writing these!

Core, utility libraries and a few plugins (like AN, Aggregator,
Poshuku and CSTP) are already ported, though not really tested.
util-x11 isn't ported yet as it requires using xcb instead of xlib
with Qt5.

Porting everything (except QML-using plugins like Blogique, LMP or SB2
or X11-dependent ones like Krigstask, Mellonetray and so on) should be
a breeze with minor fixups here or there. I've also added
util/sll/urloperator.h to hide the differences in URI query handling
between the Qt versions, and util/models/rolenamesmixin.h to abstract
away the differences at role names between the two.

Probably someone would want to help with porting? :)

Thanks.

--
Georg Rudoy