Bump paperclip to 3.4.1

Fixes #2963
Latest Paperclip requires that attachment styles has symbolized keys
Bump httparty dependency to 0.11
Bump rabl and versioncake to latest versions
Bump acts_as_list, ffaker, json and stringex to latest versions
fixes order hook logic to run hooks when finalizing order

Fixes #2986
Add expected and actual as required CONTIRBUTING.md steps
Shipments.js needs to use Spree.url to ensure api token is passed. [Fix #2989]

fixes #2990
Remove duplicate stringex dependency from backend
[backend] Symbolize image attachment style keys before running images_spec