At this point the loader in lodel/plugins/multisite/run.py is theorically
complete & correct. But some features are missing in order to be able
to test & debug it ( refs #275 ).

Deleting code from old standalone server

Seems to works !! :)

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

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

- 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