add helper for fetching status code
rewrite assertions with new error messages
improve common scenarios

 - add user cases for associations that do not exist
 - use new assertions and error messages
generate devices with a unique IP and MAC
add helper for generating required fields in a voicemail
customize firstname and lastname generated for a user
use new assertions in call logs
use new assertions in configuration tests
fix styling issues
add missing device tests
add missing extension tests
add missing tests and use new scenarios
add missing tests to lines
add missing tests to user cti profiles
use new assertions and scenarios in user line
use new scenarios and assertions in user voicemail
add missing tests to voicemails
user new assertions in user tests
fix styling issues in __init__