+ bugfixes in show_object_detailled

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

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

Adding a cache for app module reducing seriously routing overhead

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

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

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

- 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)

Regression may have been introduced about MONOSITE mode

+ uses the changes in the preload method

- found a way to make it implements the socketserver.ForkinTCPServer features reducing the global code size (and removed a lot of dirty copy & paste from cpython sources)
- deleted useless imports

- updated scripts etc
- make tests pass

- I do not understand wy the set test for Settings was OK before...