In-app workflow for contributing chords

[bragefuglseth]

Let's utilize the new fallback algorithm to make it easier to contribute chords to the database!

Here are the things needed to accomplish this:

• Database mode
• A system for mentioning when a chord should be added
• Guidelines for doing so with the database mode

Database Mode

A special mode the app can be started in that lets you add new chords to the database. Plot a chord into the diagram, let the algorithm identify it, and press a button to add it to the internal representation of the chord database. Save the database to a file again directly from the app, commit and open a PR. Easy peasy!

In addition to this, we should have a label appear in the app when the algorithm is used: "This chord is not in the database. Should it be?" The "Should it be" is a hyperlink to a section in the README here on GitHub that instructs on how to use the database mode in simple terms.

[bragefuglseth]

Not sure if this is needed anymore, closing.