Remove pyobjc from Python API, making it an 'extras_require' package. Use osascript for authentication and change how colors are encoded to not require AppKit to decode them. Users on existing versions of iTerm2 will continue to need pyobjc to decode triggers with colors, so I'm bumping the major version of the library since it is a backwards-incompatible change. Auth should continue to work as usual. Inspired by issue 10136