Add API Error Handler (#74)

* Add error handler that converts from rpc.Status errors to Watchtower API errors.

* Better testing for ErrorHandler.

* Rename testcase and remove empty default switch case.

* Change the error status back to int64.

* Converting everything to int32s.

jsonpb wraps int64s as a string which we dont like.  We'll figure out how to use values larger than int64s when it comes up.

* Remove special casing for TraceId which isn't needed anymore.

* Removing wrappers from error details since we never need to know when they are set or unset from the end user.

* Using the helper error functions inside the project service.

* Correct usage of hclog, replace panic with Error log.

* Adding periods to all API returned errors, correct spelling, fix missed invalid argument error not using helper function.

* Change our logged errors to Error instead of Warn.

* Add TODO for defining and using our own defined API error codes.

* Add TODO to remove internal error messages.

api/error.gen.go

@@ -13,7 +13,7 @@ type Error struct {
 	defaultFields []string
 
 	// The HTTP Status code applicable to this error
-	Status *int64 `json:"status,omitempty"`
+	Status *int32 `json:"status,omitempty"`
 	// An application-specific error string
 	Code *string `json:"code,omitempty"`
 	// A human readable explanation specific to this occurrence of the error