refactor(montage.py): use os.path.join instead of string concatenation
refactor(thumbnail.py): use os.path.join instead of string concatenation
refactor(uploader.py): use os.path.join instead of string concatenation
refactor(uploader.py): add support for client_secret.json file with different names in credentials folder
docs(readme.md): update instructions for openai and unsplash keys
docs(readme.md): update instructions for google oauth client id json files
docs(readme.md): add information about channel.yaml file in each channel's folder
feat(generators/montage.py): add check to skip slide if it already exists
feat(generators/montage.py): add support for DEEPL_ACCESS_KEY and UNSPLASH_ACCESS_KEY environment variables
feat(generators/speak.py): add support for Johanne voice
feat(generators/speak.py): add emotion parameter to generate_voice function
feat(generators/uploader.py): add success message and authorization prompt message to run_local_server method
fix(main.py): check if credits is None before writing to meta.txt file
feat(prompts/marp.md): change theme to gaia and add lead and invert classes
refactor(montage.py): remove unused srt_fr variable
refactor(montage.py): remove saving of french subtitle file
refactor(main.py): remove unused translate import and function call
