+ bugfixes in show_object_detailled

the get scenario produce all the get available for each instances in the site

get_referenced method were implemented for SingleReference and MultipleReference class
They are able to return LeObject instances refereced by them

Mongo sux ?

solves #185
typo fixing

Adapted to the new LodelContext

Hook names were wrong

Only run steps if count > 0

forget to name the argument

Now when we try to update an object that do not exists a 404 is answered and not a 500 anymore

Deleted old methods that are unused (one of them was triggerring an error will doing nothing)

Now we are able to limit the number of spawned child processes

Now listening address, listening port and max_children count can be configured using the Settings module

Added a sleep 1 between each background process starts.

Adding a cache for app module reducing seriously routing overhead

deleted trailing ',' from multivalue values

Now all "empty" values are deleted from the resulting array

There were manual import through importlib, we have to replace them with LodelContext calls.
Actually the plugins module is in a dirty state....

Replace some old pure python import by LodelContext calls
Change the plugins imports methods to use LodelContext instead
Fixes dyncode exposure method

added a default value for Subsection parent field

adds a default value to Publication collection field

**kwargs was not given to super() constructor

Implements a new exception class for webui : HttpErrors that uses a new template : errors.html to display multiples errors