Updated form_dropdown() in form_helper.php

The form_dropdown() function will now generate an id based on the name
attribute passed to it.

Added a demo of this on the form_helper page.
Made a copy of url_helper.php

Copied url_helper.php from /system/helpers and put it in
/application/helpers.
Modified form_anchor() function

Removed the part that puts the URL as the anchor text if the $title
variable is blank.  This logic might work great for links to websites,
however, in the web applications I build, it is more of a nuisance than
a convenience.  If I really need to, I could hard-code a link to a
website as the 2nd parameter anyway, but more often than not, I will not
need this feature.