Enumerate letters by letter files instead of from annotations

[techgique]

Currently, the list of letters page is enumerated by retrieving ALL annotations in the system and looping through them to generate the list of letters. This will be more and more inefficient as more annotations are created and more are from letters already completed and no longer in the Annotonia letters directory.

Change to loop through letter files and retrieve their annotations per letter or a query that retrieves all of the present letters' annotations.