PyPew should store Anthem details to reuse them if an anthem is repeated

[kroll-101]

Some anthems come around on an annual (or more frequent) basis.

Once #51 and #52 are implemented, it would be helpful if PyPew started storing the values for future use. (Note, will likely require some care if implementing the 'Anthem text at NEH: XXX' feature too.

UX for this might look something like the following, but open to input and suggestions:

• Above anthem entry fields have a dropdown, or better yet a type to search, which can filter on composer name and anthem title.
• -- This should return a 'Anthem not found' prompt if there are no matches.
• If a saved anthem is found, clicking on it will pre-populate the Anthem fields in PyPew, so that:
• -- If it is the same anthem text but a different composer, the user can then edit the few relevant fields and save it as a new anthem, without inputting everything from scratch.