adding a SlideType enum that can parse from a string

This will start to allow us to have a much better data model for the
slides and service items. They can have a type associated with them
and parse which they are from this type.

src/rust/lib.rs

@@ -14,4 +14,5 @@ pub mod songs;
 pub mod utils;
 pub mod video_model;
 pub mod ytdl;
+pub mod slide_types;
 // mod video_thumbnail;