Merge pull request #448 from magento-folks/bugfix

Fixed issues:
- MAGETWO-56866: [GITHUB] Custom option prices unexpectedly change after save #6116 #6342
- MAGETWO-58873: Cannot receive shipping quotes via the admin panel or front end
- MAGETWO-55216: Reference by name to non existing plugin lead to Di compilation failure
- MAGETWO-58958: Fatal error in console in flow for apply new Scheduled Staging Update using CRON
- MAGETWO-55924: [FT] Test fails because of unexpected alert window
- MAGETWO-58664: [GitHub] Free shipping rule with table shipping method breaks checkout #6346
- MAGETWO-58849: [GitHub] Error in product edit page after disable Review module #6704