serialize rationals correctly and move block name to a node input

Since rationals aren't a known Qt format, the QVariant container can't
automatically convert them to and from strings (for XML serialization). We have
to hijack these functions and do the conversion manually for those types.

Also moved the block name type to a node input, which means it's serialized
and copied by default (I'm not sure why it wasn't already like this).

app/node/block/block.cpp

@@ -28,6 +28,11 @@ Block::Block() :
   previous_(nullptr),
   next_(nullptr)
 {
+  name_input_ = new NodeInput("name_in", NodeParam::kString);
+  name_input_->SetConnectable(false);
+  name_input_->set_is_keyframable(false);
+  AddInput(name_input_);
+
   length_input_ = new NodeInput("length_in", NodeParam::kRational);
   length_input_->SetConnectable(false);
   length_input_->set_is_keyframable(false);
@@ -160,14 +165,16 @@ bool Block::is_reversed() const
   return speed() < 0;
 }
 
-const QString &Block::block_name() const
+QString Block::block_name() const
 {
-  return block_name_;
+  return name_input_->get_standard_value().toString();
 }
 
 void Block::set_block_name(const QString &name)
 {
-  block_name_ = name;
+  name_input_->set_standard_value(name);
+
+  // FIXME: Signal the name has changed to update UI objects
 }
 
 rational Block::SequenceToMediaTime(const rational &sequence_time) const
@@ -190,11 +197,6 @@ rational Block::MediaToSequenceTime(const rational &media_time) const
   return (media_time - media_in()) / speed() + in();
 }
 
-void Block::CopyParameters(const Block *source, Block *dest)
-{
-  dest->set_block_name(source->block_name());
-}
-
 void Block::LengthInputChanged()
 {
   emit LengthChanged(length());