Adding images support for doxygen documentation ( in doc/img ) + automated images generation with graphviz & make

Now we have a main page on doxygen

Deleted the classinstancemethod decorator because of inheritance problems (not sure they were real...)
Add a shortcut method to LeFactory to get the generated LeObject class
+ bugfixes

Creating a class RandomEm in EditorialModel/randomem.py

Mostly about the changes on types hierarchy

Added Lodel/settings/migrations.py that I forget
Disabled the --merge option that was given to the makemigrations command by the MH

On se base sur gettext, mais avec l'utilisation d'une langue par défaut qui sera obligatoire lors de la création de la chaine.

Behaviour changed for EmComponent and childs create method :
	- Takes care of duplicated names at creation
	- Handle all the checks in EmComponent method
Factorization of EmField.get_class_table() method
Added a @property method class_table_name to EmClass

Now an MlString instance is able to say if another MlString instance is equivalent using mlstr1 == mlstr2