implemented base transition support

While very much incomplete, transitions can now be created and will render
correctly.

app/node/block/block.cpp

@@ -22,6 +22,8 @@
 
 #include <QDebug>
 
+#include "transition/transition.h"
+
 Block::Block() :
   previous_(nullptr),
   next_(nullptr)
@@ -159,8 +161,16 @@ rational Block::MediaToSequenceTime(const rational &media_time) const
 void Block::CopyParameters(const Block *source, Block *dest)
 {
   dest->set_block_name(source->block_name());
-  dest->set_length(source->length());
   dest->set_media_in(source->media_in());
+
+  if (source->type() == kTransition && dest->type() == kTransition) {
+    const TransitionBlock* src_t = static_cast<const TransitionBlock*>(source);
+    TransitionBlock* dst_t = static_cast<TransitionBlock*>(dest);
+
+    dst_t->set_in_and_out_offset(src_t->in_offset(), src_t->out_offset());
+  } else {
+    dest->set_length(source->length());
+  }
 }
 
 void Block::Link(Block *a, Block *b)