[FIX] Always process manifest file at the end of the process since its content depends on others filers"

[FEA] Add image injection twice test

      different names, using the order parameter

fixed wrong type conversion for numeric variables.

Approved-by: Houzéfa Abbasbhay <houzefa.abba@xcg-consulting.fr>
Approved-by: Alexis de Lattre <alexis@via.ecp.fr>

Taken from https://bitbucket.org/apertoso/py3o.template/commits/fb901715731d041d28e9d86e380029cde74bc2a3?at=default.

FIX image injection test and update documentation

Keep aspect ratio of images by default

[DOC] URL now points to latest version of tree (was pointing to a very old version)

Approved-by: Florent Aide <florent.aide@gmail.com>

Nice error msg if missing equal in py3o instruction