Switch to a better DropBox API PHP class

It is clear from some of the other open issues that the current DropBox PHP class that is in the module (the DropboxUploader by Jaka Jančar - https://github.com/jakajancar/DropboxUploader/) is no longer meeting this module's needs. To that end, three of us decided to port the module to utilize the Dropbox API PHP class by "BenTheDesigner" (https://github.com/BenTheDesigner/Dropbox).

I'll include the patch in the first comment below, so far, it looks like it is working, but obviously further testing is needed. There are some tasks that we still need to figure out though, including:

1. Add some help text to the DropBox "add destination" settings page.
2. Figure out if we're handing the 32-byte encryption key stuff correctly.
3. Figure out if we're doing the autoloading of the DropBox API PHP classes the "Drupal" way.
4. Create README.txt file
5. Run the module through Coder.

If this patch does get accepted, please attribute it to not only myself (ultimike: http://drupal.org/user/51132) but also:

• cachee - http://drupal.org/user/1531834
• dhercjr - http://drupal.org/user/2252706

The three of us attacked this issue as a team (basically pair-programming the entire day, but with three of us. What's that called? Trio-programming? Tri-programming?)

Thanks,
-mike