Adds sapp back into release.

Biggest changes since last release (non-exhaustive):

• Fixed support for nested recursive function.
• Fixed several issues where the type of globally-accessible values are erroneously locally refined.
• Support batch type lookup query pyre query "types(...)".
• Support basic variadic generics on functions & classes.
• Added a safe_cast that functions similar to typing.cast but enforces subclass.
• Fixed several issues with search path construction & error filtering.
• search_path configuration now allows entries of the form { "site-package": "XXX" }
• Support specifying relative paths in binary, typeshed, and ignore_all_errors.
• Special placeholder ${SOURCE_DIRECTORY} can be added to exclude configuration to allow relative path matching in exclude configuration.
• Improved the quality of pyre-infer annotations.
• sapp is no longer bundled.