Remove the included copy of PHPMemcachedAdmin

We should be able to download this during provisioning the first time rather than including so much code that isn't ours with our repository.
Download PHPMemcachedAdmin during provisioning with wget if not available

Downloads a copy of PHPMemcachedAdmin during provisioning if the directory for memcached-admin does not yet exist, extracts that copy, and then cleans up.

Also modifies gitignore to ignore the entire memcached-admin directory now rather than just the temp files.
Add comments for phpMemcachedAdmin installation