The new layout template editor needs to be improved

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.2.1
• Fix Version/s: 3.0 M1
• Component/s: Editors > Layout Template
• Labels: None

• NPE appears when switch from empty source view to preview view.
• When the sum of weights is not 12 ( for portal 6.2 and later ) or 100 (for portal before 3.2), the preview is not correct, shouldn't fill the entire row.
• nested columns aren't shown correctly.