Erik r 2359 formatter refactored

 refactored date formatting functions

- removed unformat methods, they do not belong here
- removed db format, which is also not purpose of this class
- refactored the whole set of methods to be simpler and better
  maintainable

More unit tests needed.

TODO:

- [ ] unit tests for date time functoins
- [ ] refactor number formatting functions
- [ ] unit tests for number formatting
- [ ] update docs
- [ ] update guide