Review coding standards on HumansTxtAdminSettingsForm

Some issues:

- Class should match filename, now we have HumansTxtAdminSettingsForm and HumanstxtSettingsForm, we should be consistent (this is the main issue)
- getFormID should be getFormId instead
- Short description of the class should be one line, so there's a line break missing between lines 10 and 11.
- getEditableConfigNames() has @inheritDoc when it should be {@inheritdoc}
- Missing comma on the return array on getEditableConfigNames()
- Markup on "humanstxt_about", has a concatenation issue, translatable string should not have dots on it to get the
in
- Some indentation and array line breaks on the humanstxt_about key.