use unique temp folder for all temporary files

(so multiple instances of the test suite can be run in parallel)
mention PIL for running test suite. mention detox.
adds screenshots to README
readme screenshots 2
screenshots
Add Retina support to filer when using easy thumbnails
more prominently show that PIL needs JPEG support
PEP8 cleanup
Changed function signature get_thumbnail_name to be compatible with easy_thumbnails supporting hires images
Update filer/admin/permissionadmin.py

Added some admin options to the folder permissions to improve usability.
Update filer/models/imagemodels.py

Removed checking for staff user when serving images 
with permissions through filer. This should be like it is 
with regular files and folders.
Merge pull request #300 from zombat/develop

Improve usability in Permission Admin and fixed download permission issue
Merge pull request #299 from jrief/retina-display

Add Retina support to filer when using easy thumbnails
Validate folder name uniqueness on folder renames on folder moves/copying.
Fix for #304: make 'copy files and/or folders' work when the current folder is the root folder.
Make sure the error message on duplicate folders works with unicode characters as well.
Merge pull request #305 from kux/issue_295

Fix issues #295 and #304
adds kux to AUTHORS
updates travis packages sources for Django 1.5
updates tox test settings