Added dropbox key/secret fields.
Added dropbox signin button.
Added dropbox oauth.
Fix protocol (required https).
Reorder the optional (for gae-init) oauth code by alphabetical.
Fixed mistyped.
Replace only first occurrence of 'http' in the beginning of the url such as:
http://ahttp.com?next=http://ahttp.com/callback (replace)
https://ahttp.com?next=http://ahttp.com/callback (skip)