Stop reactor gracefully on QApplication quit

[estan]

If the reactor is running after the QApplication has quit, stop it and run all pending timed calls one last time. This will also allow the 'shutdown' system event to trigger properly, which ReactorBase uses internally to stop its threadpool.

Example:

from __future__ import print_function
from sys import argv

from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QTimer

import qt5reactor

if __name__ == '__main__':
    app = QApplication(argv)

    qt5reactor.install()

    from twisted.internet import reactor

    reactor.addSystemEventTrigger('before', 'shutdown', lambda: print('before'))
    reactor.addSystemEventTrigger('during', 'shutdown', lambda: print('during'))
    reactor.addSystemEventTrigger('after', 'shutdown', lambda: print('after'))

    QTimer.singleShot(1000, app.quit)  # Quit app after 1 second.

    reactor.run()

Before, this would not print anything. After this change it will correctly print:

before
during
after

[sunu]

Hi @estan,

This looks good to me. But this reminds me that we don't have anything similar to gtrial and GUI tests from qtreactor yet.

For now, I'll just check whether trial is satisfied or not and merge. I have added issues #3 and #4 to improve the current state.

[estan]

Excellent.

[sunu]

Thanks @estan!