Fix broken links to wiki. Fixes #1004

  * Added back ScalaDependencyInjection to docs - which had been
    deleted from both the repository _and_ the wiki.
  * The wiki has previously been absorbed into the repository. This
    patch changes all external links to the wiki into the correct
    internal links.
Documentation: Fix typos
"Fix" incorrect references to previous Play versions

  * Fix some old versions in documentation
  * Fix an old version in a test
  * Note: These Play version numbers (and possibly others) will still
    need to be updated prior to each new release.
Documentation: Add back ommitted data that code referred to

  * This data was accidentally ommitted when converting a blog post
    into documentation.
Merge pull request #1237 from greenrd/cleanup

Various doc and string fixes