fix(generators/ideas.py): fix typo in variable name 'existing_ideas'

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

prompts/marp.md

@@ -1,6 +1,8 @@
 ---
 marp: true
-theme: default
-class: invert
+theme: gaia
+class: 
+    - lead
+    - invert
 backgroundImage: url(https://images.unsplash.com/photo-1651604454911-fdfb0edde727)
 ---