* 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
* Start actually computing AppliedPatchSet values
* Improve patch_apply documentation and flesh out applied patch code
* Add file link notes
* Stub out where tests for snapshot subsystem will go
* Create baseline tests
* Fix build failure by silencing Clippy
