When the list is empty new_rank is > get_max_rank, because get_max_rank returns -1

Now modify_rank don't raise anymore when too big/small modifier is given but do its best to make a valid modification
The modify_rank tests (and the __hash__ __cmp__ tests) has been modified to fit this new behavior

Code cleaning, commenting etc needed...

The check is done on the __class__.__name__ attr of model argument (maybe not a good solution ?)

Addding a method to indicate the end of a component initialisation phase (used in Model.load and Model.create_component)
Adding a method that dump component attributes (used in Model.create_component and Model.delete_component to call the migration_handler)

No extended checks was done. Only tested if the check passes without syntax error and without failing with no reason

EmComponent::check() always return True but rearrange ranks if they are not continuous

Model._components now contains only one dict ( 'uids' key ) and the others are now list of EmComponent instances
Model now handle EVERY access to the _components dict

There is now two methods Model.name_from_emclass and emclass_from_name that allows to access the Model.components array

Changed beahvior : when a 'non-change' is asked (like +0 -0 or set ranke to actual rank) don't raise an Error

Implemented __hash__ and __eq__ for EmComponent (based on class name and uid) to test equality betwenn two instance. Allows to use "instance in instance_list" syntax