Add support for using QEventLoop inside of QThread

[kormax]

I've been doing some hacks to allow running QEventLoop of QThread myself, but seeing a nice and simple solution proposed in #122, I'd like to introduce it into the codebase proper.

As for the details:

• eventDispatcher is available for both QApplication and QThread;
• processEvents does not have a default argument value for QAbstractEventDispatcher, so we use the same AllEvents(0x00) value as in QApplication.
• exit method is available for both both QApplication and QThread, so we use it without any changes;

[hosaka]

Great stuff, thanks @kormax for addressing #122