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).
Since we load in a separate thread, when the QObject based objects are
instantiated, they're created with affinity to that separate thread. Now we
specifically ensure they are moved to the main thread after their creation.