v4.2.6

• fix #1784 removable:true working by itself (without needing acceptWidgets:true)
• fix #1791 removed drag flicker and scroll issue. Thanks @nelsieborja
• fix #1795 save(false) will no longer have .content field (removed existing one if present)
• fix #1782 save(false, false) now correctly saves nested grids
• fix #1793 save(false, true) followed by enable() throws error. we now have new Utils.cloneDeep()