OO-470: merged containers are transient with an init method to initialize them after deserialization

OO-291:  enhance the main search function for groups, add search in waiting list, add search of public group, add unit tests

OO-291: first step: move business gourp manager to a business group service, remove dependency to the context...

OO-157: optimization of WebDAV, reduce the number of DB queries with lazy loading, specific resolve method, lazy loading of quota...