core: default initialize units-type objects to 0

Makes the code much nicer to read.

Default initialize cylinder_t to the empty cylinder.

This produces lots of warnings, because most structure are now
not PODs anymore and shouldn't be erased using memset().

These memset()s will be removed one-by-one and replaced by
proper constructors.

The whole ordeal made it necessary to add a constructor to
struct event. To simplify things the whole optimization of
the variable-size event names was removed. In upcoming commits
this will be replaced by std::string anyway.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/videoframeextractor.cpp

@@ -70,7 +70,7 @@ void VideoFrameExtractor::processItem(QString originalFilename, QString filename
 
 	// Determine the time where we want to extract the image.
 	// If the duration is < 10 sec, just snap the first frame
-	duration_t position = { 0 };
+	duration_t position;
 	if (duration.seconds > 10) {
 		// We round to second-precision. To be sure that we don't attempt reading past the
 		// video's end, round down by one second.