Partial support for Image Transport and Message Filters

Fixed a bug in the model extraction process, where too many links between nodes and topics were generated.
The model extractor now unifies multiple unresolved topics with the same message type.
The model extractor only replaces unresolved topics with topics from user-provided hints.
Dependency packages and launch files are loaded lazily.
Added a work-in-progress database of pre-parsed nodes for distribution packages.
Added partial support to extract message_filters::Subscriber, image_transport::Publisher and image_transport::SubscriberFilter.
Fixed a crash that would occur when running haros from source code.
Added a unique ID to exported JSON entities of the extracted models.

git-afsantos / haros