Added a small snippet to give users a descent error message,

when their start date is afer the stop date.
Also updated the tests.

freqtrade/configuration/timerange.py

@@ -103,5 +103,7 @@ class TimeRange:
                         stop = int(stops) // 1000
                     else:
                         stop = int(stops)
+                if start > stop > 0:
+                    raise Exception('Start date is after stop date for timerange "%s"' % text)
                 return TimeRange(stype[0], stype[1], start, stop)
         raise Exception('Incorrect syntax for timerange "%s"' % text)