qt5: fix a build issue with osx and qtdbus

See comment in notificator.cpp for details.
qt5: split out qt config and add qt5 support

Qt5 detection is a big ugly mess, but at least we can fence it off.
qt5: Use the info gleaned from configure for plugin importing
qt5: Use QT_SELECT for debian-based distros.

At least Debian/Ubuntu use 'qtchooser' for switching between qt4/qt5 binaries.
It is a wrapper for all qt tools, and calls the named tool of the default
version unless overridden by the -qt= option or QT_SELECT environment variable.
QT_SELECT is set by configure once the qt version has been chosen.

Take for example, moc.

$ which moc
    /usr/bin/moc

$ ls -go /usr/bin/moc
    lrwxrwxrwx 1 9 Jul  3 21:33 /usr/bin/moc -> qtchooser

$ qtchooser -print-env
    QT_SELECT="default"
    QTTOOLDIR="/usr/lib/x86_64-linux-gnu/qt4/bin"
    QTLIBDIR="/usr/lib/x86_64-linux-gnu"

$ QT_SELECT=qt5 qtchooser -print-env
    QT_SELECT="qt5"
    QTTOOLDIR="/usr/lib/x86_64-linux-gnu/qt5/bin"
    QTLIBDIR="/usr/lib/x86_64-linux-gnu"

$ moc -v
    Qt Meta Object Compiler version 63 (Qt 4.8.4)

$ QT_SELECT=qt5 moc -v
    Qt Meta Object Compiler version 67 (Qt 5.0.1)

This should be harmless elsewhere.
qt5: tests: Make sure static plugin symbols are pulled in

Since we're now properly linking against static plugins for qt binaries,
we need to ensure that they're Imported properly.

Without these Imports, the linker drops some of the unused linked libs, causing
undefined symbols in QtCore.
qt5: Force macports default include path to be searched last

Allows outside includes to take precedence. In particular, this allows for
a specified Qt to be used without clashing with macports' headers.