Added values list to generated classes

[vsly-ru]

What does this change?

This PR implements a feature requested in #186. It adds values getter at the end of generated classes for directories with the list of all statement' names.

Possible problem:

Name collision of values with an existing asset. Feel free to suggest some less generic name so I'll rename it (or simply edit it yourself). I just don't have any ideas about naming conventions for a predetermined field for this project.

Possible improvement:

Make this list optional with some flag.

[stefanschaller]

Like it! Would be great for caching icons. @wasabeef

[JulianBissekkou]

I was about to implement the same feature, because I need this for 2 of my projects! Great work. @wasabeef Can you take a look and provide feedback to this PR?

[wasabeef]

@vsly-ru

Thank you for your PR, I released v5.0.0 and v5.0.1. The version includes the values list feature.

cc: @stefanschaller @JulianBissekkou