add find_by_extension_id to line_extension service
refactor user voicemail tests. Regroup common prerequisites
add find_by_voicemail_id in user_voicemail service
add find_by_user_id to user_voicemail
remove ULE usage in device service
remove ULE usage in user_line
fix pep8 warnings
remove ULE usage in user_voicemail
fix pep8 warnings
remove ULE usage in user service
delete user_line_extension service
add ULE helper to setup.py