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

Before we were calling the logging.getLogger function without argument. The result was
that all contexts were sharing the same logger (and every message were logged X time with
X the number of loaded context).
Now getLogger is called with the context id as argument, each context has its own logger.

WARNING : not fully tested

Now the loader context is threated like the others (it loads it's libs from a symlink, before it was loading them from lodel package)

a bit dirty & quick

They were a bug when ordering stuff contains 2 values that are equals

was disabled for debugging...

Previous bugfix on runtest & create instance brokes deployment, now both seems to work fine

- a "normal" import was left in lefactory_common
- the hook triggering datasources init in dyncode was not called
- dyncode was not exposed in the loader (making hook call useless : the hook has to be called once the dyncode has been "seen" (imported) by python)