Changes in flags for UI
- Removed the `--ui_packaging_path` flag which was slightly confusing, and instead added a new output format (`--output_format ui`), which makes more sense as the UI merely consumes another form of output form iCatcher+.
- Input videos are not copied to output when ` --output_format ui` is passed, as this is redundant (frames are being produced, and if user needs an annotated video there are other options for that).
- Adds some basic tests for this option, and updates the README / docs accordingly