Defer string -> timedelta conversion to get_onion_class
Defer string -> timedelta conversion to get_onion_class

Also, standardize naming of classes to match crawler.py

freedomofpress/fingerprint-securedrop,freedomofpress/FingerprintSecureDrop,freedomofpress/FingerprintSecureDrop,freedomofpress/fingerprint-securedrop,freedomofpress/fingerprint-securedrop