support multiple snippet lists

[Benjmhart]

the user might want to supply files to be used

1. change state to a cursor of cursors
2. swap out cursor structure to allow cursor to be empty (point at nothing)
3. 3 process multiple files as arguments
4. allow a config file to be read (Yaml) which specifies the list files to be used.

[Benjmhart]

add controls for moving the current snippet to the left/right and moving it up and down

add a control to introduce an empty block in the current queue