Isolated exception handling from donor repository & controller(#215)

-- Removed catching Exceptions from donor repo and controller
-- Modified Test cases to expect Exceptions instead of Null
-- Added New Exception handling methods on GlobalExcpetionHandler
Improved Exception handling on usage (#215)
Improved Exceptional handling on donations (#215)
Improved Exceptional Handling on Requests(#215)
Improved Exceptional handling on products (#215)
Improved Exceptional Handling on locations (#215)
Fixed issue on donor & donation repository (#215)
Improved service layer exceptional handling (#215)
Added 2 more exceptions & Removed 1  not thrown Exception(#215)
Removed  unused exception handling methods (#215)
updated donor test cases names (#215)
Improved requests controller exceptional handling (#215)
Modified  to handle More specific exceptions (#215)
Updated comment (#215)
isolated Exceptional handling from user controller (#215)
Merge branch 'Adapt_BSIS_to_expose_REST_services_#209' into Improve_Controller_Exception_Handling_#215
Isolated NumberFormatException (#215)
Added global JsonMappingException(#215)
Ordered exception handlers(#215)

-- Added new InvalidFormatException Handler
-- Ordered handlers
More verbose Error formats(#215)