Improve the error output for incorrect usage of page objects

Author: mdmintz

seleniumbase/common/exceptions.py

@@ -1,5 +1,6 @@
 """ SeleniumBase Exceptions
     NoSuchFileException => Used by self.assert_downloaded_file(...)
+    OutOfScopeException => Used by BaseCase methods when setUp() is skipped
     TimeLimitExceededException => Used by "--time-limit=SECONDS"
 """
 
@@ -8,5 +9,9 @@ class NoSuchFileException(Exception):
     pass
 
 
+class OutOfScopeException(Exception):
+    pass
+
+
 class TimeLimitExceededException(Exception):
     pass