[#6314] Changed ShortURLs to be unique to the app instance instead of globally unique

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6314] Add config option for short_url.url_pattern and refactor short url form widget

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6314] Refactored, added tests, and removed hard-coded nbhd from ShortUrl

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>