Faster dependency reload

[piercefreeman]

Our initial implementation of hot reloading worked in most cases, but there were some edge cases where it failed to update nested closures (including typehint schema changes for new controllers). It was also a bit slow on large projects since it needed to traverse modules that were in memory dynamically during every reload. Our new approach constructs a DAG of dependencies based on traversal of the project's AST. When we detect that a file has changed we just need to consult the current graph of file dependencies and traverse them in order to resolve all modifications. This also has the benefit of making our logic easier to unit test because it separates out dependency construction from the reload process.