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

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

Regression may have been introduced about MONOSITE mode

- updated scripts etc
- make tests pass