Removed useless readonly property on some fields

When not found return None and do not try to run len() on None

Add master = true to uwsgi.ini

Add the custom message provided by HttpException to the template

Pymongo do not handles sets as value. We have to cast them into lists
done only in update for the moment...

Return an instance and not a list of len 1 anymore

In construct and check data

Add the possibility to give a fixed name to instances created by mass_deploy

Tree 'scenario' are available :
- mass insertion
- mass edition
- mass deletion
For the moment scenario parameters and order are harcoded :
- 50 iteration for mass_insertion
- 10 iteration for mass_edition
- 10 iteration on deletion

mass_deploy now warns you when using $RANDOM instead of pwgen or /usr/share/dict/words