Checkmk Werk 7775: Fix some NagVis maps snapin tree rendering issues

ID: 7775 Title: Fix some NagVis maps snapin tree rendering issues Component: Multisite Level: 1 Class: Bug fix Version: 1.7.0i1 The NagVis maps snapin can be configured to be rendered as tree (by configuring the global setting "multisite_snapin_layout" in NagVis). The fold arrows rendered in the NagVis snapin were not displayed correctly in 1.6.0b1. The rendering has now completely been cleaned up to be working as expected again. The folding state was never remembered for this snapin which has also been fixed now.