* domain-model pattern

* fixed optional get before check isPresent

* readme minor changes

* change currency representation with joda money

* changed names of test methods

* fixed code smells

* Update domain-model/README.md
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>

* Update domain-model/README.md
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>

* updated readme and diagrams
Co-authored-by: NIlkka Seppälä <iluwatar@users.noreply.github.com>