Added single scan get w/ errors

ref #67

src/errors/ScanErrors.ts

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