[INTERNAL] sap.m.P13nColumnsPanel - small changes

+ destroyItems added in P13nXXXPanel
+ P13nDialogItem deleted
+ rerender optimized in P13nDialog

Change-Id: I56eb9fabe9e76d1b5cdf1a4920b0c55728ccff4d
Merge "[INTERNAL] sap.m.P13nColumnsPanel - small changes"