Improve handling of panels drag&drop

[mitar]

Currently drag&drop of panels has quite some issues:

• Ajax requests to store their position is send many times while window resizing, it should be send only at the end
• window is currently much to high (it should collapse if columns are getting shorter because user moves a panel around)
• panels should not fluctuate around while user is resizing the window, but stay where they are and only rewrap if window becomes wide enough for more columns, but then again stay stable

One feature to discuss:

• if user moves panels around, should they also move in all other windows user might have open at the same time? in some way this would happen if she would reload those windows, as new state is stored, so doing that without reloading is plus, but on the other hand it will disallow user to have different configuration in different windows (maybe she wants one window with more funny stuff and one with more serious panels), but then this our state saving does not support anyway