refactor SoledadCrypto to remove circular dependency with SoledadSecrets
Why SoledadCrypto depends on Soledad? https://github.com/leapcode/soledad/tree/develop/client/src/leap/soledad/client/crypto.py#L167 It only uses it to get SoledadSecrets: https://github.com/leapcode/soledad/tree/develop/client/src/leap/soledad/client/crypto.py#L215
SoledadSecrets depends on SoledadCrypto, is this circular dependency really needed? https://github.com/leapcode/soledad/tree/develop/client/src/leap/soledad/client/secrets.py#L148
(from redmine: created on 2015-08-04, closed on 2015-08-05)