ISSUE-10: Add unit tests

[fraenky8]

This PR fixes #10 and does the following:

• [x] Refactor the packages to use DI and therefore enable proper unit testing
• [x] Add unit tests for the Run() function for every supprted database and its datatypes:
  • [x] String/Text data type
  • [x] Integer data type
  • [x] Float data type
  • [x] Temporal data type
  • [x] Special data types like booleans
• [ ] Add unit tests for all other files including
  • [ ] databases:
  • [ ] mysql
  • [ ] postgresql
  • [x] outpts:
  • [x] decorator
  • [x] writer
  • [x] tagger:
  • [x] db (covered by standard Run() function)
  • [x] mastermind
  • [ ] sql
  • [x] settings
• [ ] Add units test for error cases
• [x] Increase overall test coverage
• [x] Add Scrutinizer support