add a 'flow' enum to approval_groups
add SimpleEnum for Rails 4 compatability
clean up approval group form indentation
Merge remote-tracking branch 'origin/master' into 79249190_linear_group

Conflicts:
	Gemfile
	Gemfile.lock
add form option for selecting linear flow
use built-in enum support form rails 4.1
validate presence of ApprovalGroup#flow
simplify select options helper
feature flag the flow
add without_feature spec helper
store approval group flow as a string
[#81500686] Add non-existent user after OAuth
validate Approval#status
simplofy signature for CommunicartMailer.approval_reply_received_email
remove usage of arbitrary param hash for approval email
remove use of @cart_template
move cart template logic into decorator
remove use of ternary operator

...for better readability and test coverage reporting
unify approval logic
add code climate badges