Resizing the browser window can freeze the resizeable panels

Left and right panel in the channel manager can be resized. But the code sometimes prevents resizing after a resize of the browser window.

Reproduction path:

• make the browser window wide
• open the right side panel and drag it to its maximum width (50% of the screen)
• close the right side panel
• make the browser window smaller (less wide)
• reload the browser
• open the right side panel again: it opens very wide and is not resizable anymore

This has somehow to do with the calculation of the maxWidth that is based on the body size. When after a reload of the app the maxWidth is recalculated but the stored width of the panel is bigger than that, the resizing is blocked. This needs a bit of brain time to figure out how to fix this.