Added first donor-specific errors

ref #65

src/errors/DonorErrors.ts

@@ -0,0 +1,25 @@
+import { IsString } from 'class-validator';
+import { NotAcceptableError, NotFoundError } from 'routing-controllers';
+
+/**
+ * Error to throw when a donor couldn't be found.
+ */
+export class DonorNotFoundError extends NotFoundError {
+	@IsString()
+	name = "DonorNotFoundError"
+
+	@IsString()
+	message = "Donor not found!"
+}
+
+/**
+ * Error to throw when two donors' ids don't match.
+ * Usually occurs when a user tries to change a donor's id.
+ */
+export class DonorIdsNotMatchingError extends NotAcceptableError {
+	@IsString()
+	name = "DonorIdsNotMatchingError"
+
+	@IsString()
+	message = "The ids don't match! \n And if you wanted to change a donor's id: This isn't allowed!"
+}