Better explain what downloads are needed on the finish page

[allo-]

Maybe wrapping all downloads other than profile.zip in a collapsed <details> and add a short explanation each when which download is useful.

• profile.zip: Most users should use this.
• enterprise_policy.zip: Limited but easy to deploy for all users. Contains the cleanest way to automatically install addons and can enforce settings for all users. Also some UI settings like always showing the menubar are not available as prefs.js settings.

These are rather there because they are easy to provide in addition, but not the preferred way to install the profile:

• prefs.js only: If you don't want to download the addons or just have a look at the settings generated similar to the preview section.
• addons.zip: The other way round. Only the addon files and not preferences. Not that useful as they won't be installed without user_pref("extensions.autoDisableScopes", 14); in the prefs.js

Issue #292 is about setting preferences with Enterprise Policies. When implemented they can probably be used as a full replacement for the zips.