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

README is now present in $(datadir)/doc/lodel2/
And as README.gz in /usr/share/doc/lodel2/ for debian packages

with make deb . Next commit will update the README

Now mass_deploy is able to stop when slim fails indicating on wich action slim fails
Bufixing webui conf edition

Before when session restore fails the webui was answering "Unknown status 200" as content.
Now it produce 2 log messages (maybe)

broken nginx conf + absolute path in slim that is known only at build time