move ci skip behaviour into a new commit_command class
skip build on "skip ci" (backwards "ci skip")
ensure message is private

TIL attr_reader can be private.  thanks @scottharvey!
Send info about ability to use secure env vars to worker

This commit sends info on availbility of secure env vars to worker.
Additionaly it allows to use secure env vars in pull requests as long as
the commit was pushed to the same repository.
Use simple states from rubygems
Add a welcome email to the first user sync.
Merge branch 'master' into mm-welcome-email
Add Blue Box logo to email footer.
Update the email source.
Lighter color for the new footer.
Update the erb template too.
Merge pull request #217 from travis-ci/ps-secure-env-vars-in-prs

Send info about ability to use secure env vars to worker
Use secure_env_enabled? and addons_enabled? when decrypting config

Using pull_request? is no longer valid, becasue we changed the rules of
secure env vars and addons availability.
Don't send welcome email if users is older than 48 hours.

Sort of a safety net in case, for some reason, synced_at should
remain empty for users.
Blank?
Use only configured address.

In the context where the messages are sent, the from address is
set to the full name and email address.
Add welcome email subject. Fix broken tests.
Track a metric when sending a welcome email.
Smaller font size for the footer.
Use logger.