Issue: Autolink generation from different namespace

For clarification on my part when we get around to this, since I keep wondering why it's needed anymore (namespaces were removed):

Provide a forum setting, and an area setting: "Auto-link terms to items that use with the following Prefix:" and a select field containing the various prefixes in the wiki.

Namespaces were removed in favor of Prefixes. Prefixes are similar in that they add to the beginning of the article name and URL, but you can select prefixes at the article level rather than restricting an entire part of the wiki to use a specific one. To allow more backwards compatibility for people who liked the restrictive nature of namespaces, there should be an option on a per-area basis that lets you choose which prefixes are available in that area.

Originally requested for 3.0.7.

I would vote for it on vW4

This has been implemented in the next release:

As before, Auto-Links are enabled for content-types "Wiki Content" and "Forum Posts" using the checkboxes in Settings > VaultWiki: Wiki Links > Enable Auto-Links to Wiki Content.

For each area, there is a new setting "Enable Auto-Links to Wiki Pages with Prefix", with a choice of:
- [Do NOT Auto-Link]
- [Match Prefix of Current Page] (note: this was the previous behavior, and thus is the default selection)
- [No Prefix]
- specific prefixes

For each forum, the new setting "Enable Auto-Links to Wiki Pages with Prefix" replaces the previous yes/no option "Enable Auto-Links to Wiki Pages". It has a choice of:
- [Do NOT Auto-Link] (note: this was the previous "No"/default behavior, and thus is the default selection)
- [No Prefix] (note: this was the previous "Yes" behavior)
- specific prefixes

The upgrade script will map the existing Yes/No values to the new forum setting. To prevent data loss on re-upgrades, existing values will not be removed in this version.

If a wiki page/post does not choose its own autolink prefix via an autolink_prefix field (note: there is not feature that does this currently, but an add-on could set the field if desired), then the area/forum setting will be used. The auto-link handler has been slightly refactored to make it easier for add-ons to extend this for other content-types.

If no setting was discovered (e.g. a blog comment from an add-on might not be in the wiki or a forum), then use the value of the new setting Settings > VaultWiki: Wiki Links > Default Prefix for Auto-Links. It has a choice of:
- [No Prefix] (note: this was the previous default behavior, and thus is the default selection)
- specific prefixes
Note that there is no "Do Not Auto-Link" option here because that is already handled by the adjacent setting "Enable Auto-Links to Wiki Content".