Plugin list on Diagnostic

[MinchinWeb]

Further to #1006, displays active plugins on --diagnostic rather than --version

[wren]

I forgot to comment on this after our conversation in #1006, sorry!

This PR is dependent on what we decide to do with versions numbers for internal plugins, so I don't think we should merge this yet. I'm going to mark it as a draft for now until that conversation is finished.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[MinchinWeb]

Not stale.

Suggested format (from here):

Formats:
    Import:
        jrnl    : jrnl (internal)
    Export:
        boxed   : fancy (internal)
        default : custom-default v1.1.0 from foo.bar.somewhere_else
        foo     : bar v1.3

1. "Formats", "Import, and "Export in the titles so it's more consistent with the docs
2. Include the name of the plugin even if it's internal
3. Only include the from foo.bar.whatever if the plugin is not at the default location (so there's less noise for the defaults)
4. Line up the colons so it's more consistent with other general output

[MinchinWeb]

Output looks like:

λ jrnl --diagnostic
jrnl: v2.8.1
Python: 3.9.7 (tags/v3.9.7:1016ef3, Aug 30 2021, 20:19:38) [MSC v.1929 64 bit (AMD64)]
OS: Windows 10

Active Plugins:
    Importers:
        jrnl     : jrnl (internal)
        json     : simple_json v1.0.0
    Exporters:
        boxed    : fancy (internal)
        dates    : dates (internal)
        default  : pretty (internal)
        fancy    : fancy (internal)
        json     : custom_json v1.0.0
        markdown : markdown (internal)
        md       : markdown (internal)
        pretty   : pretty (internal)
        rot13    : rot13 v1.0.0
        short    : short (internal)
        tags     : tag (internal)
        test     : flag v0.0.1
        testing  : flag v0.0.1
        text     : text (internal)
        txt      : rot13 v1.0.0
        xml      : xml (internal)
        yaml     : yaml (internal)

Tests appear to be failing because the skip tags aren't working, but that is beyond the scope of this PR (adjusting plugin info display). Also, Windows tests don't appear to run at all.

---

I think it's ready to merge.

[wren]

Looks good. Thank you for making the updates!