Rework get and find editions

[peterstadler]

Description, Context and related Issue

When adding an edition file as test data to the testing/XQsuite/data collection the Edirom would automatically pick up this "edition". This PR rewrites the functions for finding (all) editions from the database (formerly edition:getUris#0, now edition:findEditionUris#0) and the function for retrieving (just) one edition by its ID or database path (formerly edition:findEdition#1, now edition:getEditionURI#1).

The notable difference of edition:getEditionURI#1 is that it now will return the empty sequence if no resolvable edition ID or path is provided. It will not magically search the whole database. If this is intended, you'll need to combine this with edition:findEditionUris#0. See index.xql where this change got necessary.

How Has This Been Tested?

Tested locally with the clarinet quintet and the Pintos data.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Improvement
• Refactoring

Overview

• I have updated the inline documentation accordingly.
• I have performed a self-review of my code, according to the style guide
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes at testing
• All new and existing tests passed.

[roewenstrunk]

Tested with Klarinettenquintett and Pintos.