remove duplicate database schema entries

[bbortt]

tldr; database normalizations.

• removed the duplicate error messages on scenario_execution and test_result
  • now only being present in test_result
• removed the duplicate status report on scenario_execution and test_result
  • now only being present in test_result
• information is still available, because of the new relationship of scenario_execution to test_result
• error information has been splitted into stacktrace and error_message (the later containing only the root cause message)
  • both fields are blobs; no more length restriction

see the updated documentation / database schema.

[bbortt]

there is one more thing I would like to take a look at:

• [x] duplicate getters in criteria api