Replace PyCrypto with cryptography.

Implement some functions for handling random generation using os.urandom
minor fix against zipfile infos
Merge pull request #213 from globaleaks/feature/cryptography

Feature/cryptography
removed safe umask concept
addressed issue https://github.com/globaleaks/GlobaLeaks/issues/828
implemented uniform_answers_delay in function interacting with session_id from authenticated users
completed time constant check in XSRF comparison
minor fixes and UT (apparently) fixed