[WIP] extracted date format converting to a helper class

adding and reworking the conversion of:
- ICU to PHP
- PHP to ICU
- ICU to JUI
- PHP to JUI

TODO:
- [ ] refactor date validator to use it
- [ ] refactor JUI date picker to use it

fixes #1551 
Can be initialized with `false`. You'll be able to remove `else` part.