Delete the old thumbnail when the author changes it
Add some dependencies about linux installation
pep8
Merge branch 'dev' of https://github.com/zestedesavoir/zds-site into delete_image_on_change
mention dependencies in doc + fix repo location
add unit test and fix the use of MEDIA_ROOT. fix bug for scenario before <=> without image, after<=>with image
fix pep8
Merge pull request #625 from artragis/delete_image_on_change

Delete image on change