rails4: gemify attachment_fu

closes CNVS-14268

Since this is very clearly our own fork of the gem at this point, I've
removed a lot of unused code, rather than fixing it up to work as a gem.
This includes:

* all the other processors besides mini_magick
  * red_artisan, it was only used by the core_image processor
  * geometry and the Array monkey patch, it was only used by image science
* the db_file_backend
* the Tempfile monkey patch, I fixed the AttachmentFu code to properly
  create tempfiles with the desired extension
* removed the Technoweenie outer namespace, to match normal gem practices

test plan:

Attachments should still work as before, including viewing, uploading,
downloading, and thumbnail generation.

Change-Id: I94ff63182af839ec54b64714defd6912b0d91f65
Reviewed-on: https://gerrit.instructure.com/41281
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>