Extend SmartlingApiException with errors from API response

[dimitrystd]

SDK is used in connectors where we want to react differently depending on actual error.
You can find error response format there. You can see that response can contain more than 1 error. Thus SDK must return array of errors in case of error.

DoD:

• Extend SmartlingApiException with array of errors
• Rewrite error handling in BaseApiAbstract. It must convert errors from json response to errors array in SmartlingApiException
• Do all changes in branch 2.0.0-g5