Merge pull request #286 from magento-mpi/MPI-bugfixes

Fixed issues:
 - MAGETWO-56344: [Github] #5902 Braintree doesn't work when using table prefixing
 - MAGETWO-55953: Exception occurs when tracking shipment with invalid FedEx tracking number
- MAGETWO-56801: [GITHUB] Fixed column description for "website_id" column #4388
- MAGETWO-56745: [Github] PayPal Express Checkout "Display on Shopping Cart -> NO" does not work
- MAGETWO-56467: Free shipping threshold fields are mixed up in UPS and Fedex configurations
- MAGETWO-56342: [Github] #5910 Braintree sandbox errors when using alternative Merchant Account ID
- MAGETWO-56115: [Github] #5857 Impossible to configure custom availability gateway validator
- MAGETWO-54134: CE module depends on EE code
- MAGETWO-56447: UPS not providing shipping rates for Puerto Rico