[SYNCOPE-546] improved model-typing in date time field panel, solved date deletion problem

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1622502 13f79535-47bb-0310-9956-ffa450edef68
[SYNCOPE-545] added management of null date, hour, minutes in date-time field panel

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1622636 13f79535-47bb-0310-9956-ffa450edef68
[SYNCOPE-545] merge from branch 1.1.X, date-time field panel only

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_2_X@1622640 13f79535-47bb-0310-9956-ffa450edef68