CMS-4480 User Manager - Password component

- unified all FormInputEl descendants .setValue methods to return element
- added get/set type to InputEl
- added NumberHelper.randomBetween
- added StringHelper.isUppercase, isLowercase and isAlphaNumeric
- also updated StringHelper tests
- created PasswordGenerator input
Merge pull request #1063 from enonic/cms-4480

CMS-4480 User Manager - Password component