[SYNCOPE-391] password management made optional, null password can be stored on Syncope internal storage

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_2_X@1609714 13f79535-47bb-0310-9956-ffa450edef68
merge from branch 1_2_X

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1609715 13f79535-47bb-0310-9956-ffa450edef68