use Spree.t on order.state

Fixes #96
Use correct path_prefix so that URLs are correct
Fix a compatibility issue with form_for as provided by other helper replacement gems.

Fixes #100
Add admin user tab translation

Related to spree/spree#3133
Use flash[:success], not flash.success

Fixes spree/spree#3166
Correct branch references to 2-0-stable for Spree components in Gemfile
Use currency in user order total.
correctly scoped translation key

Fixes #104
remove double quotes to match format of other strings

Related to #104
Upgrade

Merge branch 'source/2-0-stable' into 2-0-stable

# By Ryan Bigg (4) and others
# Via Ryan Bigg
* source/2-0-stable:
  remove double quotes to match format of other strings
  correctly scoped translation key
  Use currency in user order total.
  Correct branch references to 2-0-stable for Spree components in Gemfile
  Use flash[:success], not flash.success
  Add admin user tab translation
  Fix a compatibility issue with form_for as provided by other helper replacement gems.
  Use correct path_prefix so that URLs are correct
  use Spree.t on order.state