Add uploaded videos to playlists

You can upload a video to a playlist automatically based on the video's label (unlabeled, overhead, etc.).
Define the mappings of labels to playlist IDs in Settings
- Playlist names are cached to reduce unnecessary API calls to YouTube that would use up quota points
- Mappings are not case-sensitive. Behind the scenes, the mapping labels and video labels (only for mapping purposes) are lowercased
Playlist additions are best-effort. Videos are still uploaded even if the subsequent playlist add API call fails
Warnings (do not block uploads) appear in the UI if:
- No playlist mappings are defined
- A video to be uploaded has a label with no associated playlist

Closes #33

gafirst / match-uploader