removed Searcher class: not used anymore
updated method index_objects: was using code for old implementation
fix search_for_class
index_update: fix key used to deleted old document
don't add 'None' value in indexed terms
index update: don't add twice the same document during a single transaction
trigger index task only if there is items to index
default view registry: url function should also accept object type and id, for cases where no instance has been retrieved from db
indexing: worked on search(). Removed 'get_models' method
added basic search view, with object type faceting
don't look in __indexation_args__ for searchable, use a separate attribute.

Easier to control indexation within class hierarchies.

Entity is not indexable, Entity subclasses are indexable by default
correct use of whoosh.query.Or
added shell command for reindexing