* Rewrite project file to have relative paths and drop SourceProject
* Redo project error types
* Tidy up and document Project type
* Strip out init command
This doesn't feel ideal. Though it's true that all directories are influenced by
any init scripts they have, the directory middleware shouldn't need to know
about Lua.
I don't really want to go back into working on the middleware chain since it
mostly feels like busywork when there are other things to build on in Rojo.
also all of this feels really complicated
* Refactor contributing_paths into contributing_sources, deleting project node sources
* Instead of changing contributing_paths, add instigating_source
* Remove InstanceMetadata::project_node
* Stop pushing project path to front of contributing_paths since it doesn't matter now
* Remove accidental UI change for path display
