[app-crypt/qca] Add qt5 supporting 9999 ebuild

Add an ebuild for QCA head which enables compiling with Qt5.

* Using CMake as (new) preferred build system, plugins are now implemented as USE flags instead of separate packages like in portage.
* Fixed qoauth ebuild to support the new USE-flag system
* Depends on https://github.com/gentoo/qt/pull/13