QGst::ChildProxy: change the signature of findChildProperty to use QGlib::Object as well

...to complete 759edbaca19a3a88bfbe74bd6e1ae6554df83e2e
QGst::AsyncDoneMessage: fix coding style of the running_time method name -> runningTime
QGst/discoverer: fix inheritance of DiscovererInfo & DiscovererStreamInfo

The real superclass is GObject, not GstObject.
QGst/memory: fix coding style issues and other minor problems

* missing > in copyright email
* doxygen comment needs to be exactly before the class it documents
* forward declaration of class Buffer is not needed
* the number of characters in a line should not exceed 100
QGst/{enums,event}: rename NewSegmentEvent to SegmentEvent, as it was renamed in GStreamer
QGst/enums: remove unneeded codegen overrides and eliminate usage of C++11-style enums
QGst/enums: remove shift constants

It's not a good idea to export them in a way that applications can use them,
since they are not part of the API and may change.
QGst::CapsEvent: add a method to get the caps
QGst::FlushStopEvent: add method to get the reset_time
QGst/event: replace qPrintable by a proper UTF8 conversion

qPrintable converts the QString to the local 8-bit encoding of
the system (usually UTF8, but can be something else), while
Glib/GObject/GStreamer always expect UTF8 strings.
QGst::QosEvent: rename type() to qosType() to avoid confusion

There is also Event::type() which returns the type of the event
and it's confusing to have different methods named the same on
the same object. The unit test already has got this wrong...
QGst::Event: fix harmless but confusing typo in the implementation of typeName()
QGst::Event: wrap gst_event_has_name()
Revert "src/QGst/pad.cpp detect pad type and chose the right pad event sending call."

This reverts commit 70807a8f52933f65db99ce7af170e880d3a9523c.

That commit looks totally wrong... gst_pad_send_event() can handle all types
of events. gst_pad_push_event() is meant to be used by elements to push
events up or down in the pipeline.
QGst::Pad: align the API for getting/setting Caps with the equivalent C API

It's not a good idea to divert from the C API and create confusion
on how these methods work.
QGst/sample: fix the coding style of Sample::create

* Respect the column limit
* Use const references for arguments, which is faster
QGst/sample: fix passing of the Structure argument in create()

gst_sample_new consumes the given structure, so we have to copy it.
QGst/sample: fix copy/paste typo in doxygen comment
QGst/sample: remove useless static_casts
QGst/taglist: cleanup header includes and move sample.h include to the .c file

In qt-gstreamer in general I have avoided so far to include many
things in the headers in order to minimize compilation time for
the users of those headers. Let's not change that here.