Zoom update at different tabs

[Jiri Srba]

Open some net and set the zoom to 200%. Then make a new net in another tab - it will show 200% for that tab but it will draw the net only at 100% zoom (until the zoom dropdown menu is updated).

The fix should be that each tab should remember its own Zoom value and when making a new tab, the default zoom level should be 100%.

This needs to be fixed both for cpn-branch but also for 3.9 series (on launchpad).