[docs] Polish contribute page, css list nits, client-config & docker fixes

[ix5]

Checklist

• All new and existing tests are passing
• (If adding features:) I have added tests to cover my changes
• (If docs changes needed:) I have updated the documentation accordingly.
• I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)
  

What changes does this Pull Request introduce?

docs:

• contrib/docs: Add live rST editor link, nit
• [nit] client-config: Mark strings with quotes
• testing-client: Update make docker cmds
• css: Indent ordered lists as well, cleanup
• contrib: More purpose-oriented TOC
• contrib: Add commit msg examples, checklist
• contrib/docs: Mention commento contrib, nits
• [nit] test-server: Correct make command

MANIFEST.in: Add Javascript .map files

Those files allow for de-obfuscating minified webpack-assembled bundles and tracing function calls back to the source files when used in browser debuggers.

Makefile: apidoc: Also render private APIs

Marking /admin and /demo endpoints as private is semantically correct, but since these docs are aimed at developers anyway, document them in any case.

contrib: Add sample cfg

To be used as a base for e.g. Docker instructions.

docs, README: Update Docker instructions

Mention the official image and be a bit more clear about config requirements.