Original version 0.5 from ShoutWiki & other tweaks

Original version 0.5 (ShoutWiki SVN revisions r2293, r2294, r2299) added
the JavaScript username existence checker & password validity checker to
the signup form, and moved the hooked functions from the main setup file
into their own file.
On top of this, I've gotten rid of the legacy (PHP) i18n file and the $dir
variable, hence why this is now version 0.6.

Change-Id: I15e4c606ac175895c4a6d605f0f2d6ae2518f846