Panel toggles and handles inconsistencies

After some testing on snapshot, here are comments/improvements that were found:
1. `when I hide a panel and then switch to "mobile mode" by making the window smaller, the panel stays hidden but there is no more button to get it back?`
2. `the padding we added to the make the panels symmetric again should be removed for "mobile mode" as they add assymetric padding.`
3. `in standalone edit mode (like when creating a page), the panel widths are applied but it isn't possible to resize the panel`