Add a logger for each model

Conflicts:
	trytond/ir/cron.py
	trytond/ir/ui/view.py
Add log when encoding is invalid
Monitor: log modified modules and error

And minor reformatting.

Conflicts:
	trytond/monitor.py
HTTP protocol patch

Conflicts:
	trytond/server.py
HTTP: improve send_error method

* add HTTP header 'Connection: close' (Closes #556)
* don't ignore 'Connection' or 'Content-Length' headers in parameter
* don't always send message
Send JSON encoded response instead of a more human readable format
HTTP: Fix inherited class order, closes #556

As stated in the doc:
The Mix-in class must come first, since it overrides a method defined
in UDPServer!