removed unnecessary hint in README
updated Gemfile.lock
Merge branch 'develop'
huge commit:
    removed feature to signup as a client autonomously (devise
    "registerable", "confirmable")
    wrote test to ensure that an admin can create a user
    adapted factories and migrations
    created user mailer and let it send welcome messages with
    credentials
@wip:
    added redirect if client has only one website
    cucumber tests broken
fixed broken tests
added one more test for the redirect in case of a single website for a
user
Merge branch 'develop'
adjusted README to the new workflow