Issue: Allow Both Edit and Source Tabs

Sometimes you don't want to fully edit an article but just copy a snippet of the code for use in another article. You might not be so comfortable opening the Edit tab in case you change something, because of the annoying message that you are navigating away from the editor, or just because you want to save the site the overhead required to load the editor.

The Source tab is ideal for this situation, but it only shows for users who don't already have access to the Edit tab.

In VaultWiki 4, we do a much better job at organizing the article's tabs with even less horizontal space (due to the sidebar), so we can fit a lot more tabs than we could with VaultWiki 3.

Source tab unlocks in 4.0.0 Alpha 1.

Originally requested for 3.0.17.