Clean up file.

- Remove redundant backslash for line continuation.
- Remove unneeded extraction of filename extension.
Change mentions of "image" with "file".
Clean up blank lines.
Add non-image file icons support. Cherry-picked from syko@75ee16e.

Conflicts:
	ckeditor/templates/browse.html
	ckeditor/views.py
File clean up.
Fix browse preview so Embed button shows up.