Increase maximum HEALPix depth

[Schneegans]

With this, we can load much more high-resolution data. Changes:

• Increased maximum HEALPix depth from 20 to 30. This reduces our minimum tile size from about 13 m to 13 mm.
• Improved the scene scaling of the default configuration to allow for a smoother navigation close to the surface.
• Fixed an issue which led to an accumulated error in the rotation quaternion of the observer.
• Fixed an issue which caused precision issues for very small movements of the click-and-drag navigation.

With this set of changes, we can go well beyond a 1:1 scene scale and actually explore map data "like an ant" in the sub-millimeter range.

[coveralls]

Pull Request Test Coverage Report for Build 4688323861

• 0 of 25 (0.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.0001%) to 1.141%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/csp-lod-bodies/src/utils.cpp	0	2	0.0%
src/cosmoscout/ObserverNavigationNode.cpp	0	2	0.0%
src/cs-core/DragNavigation.cpp	0	21	0.0%
<!--	Total:	0	25	0.0%	-->

Files with Coverage Reduction	New Missed Lines	%
plugins/csp-lod-bodies/src/utils.cpp	1	0%
<!--	Total:	1		-->

Totals
Change from base Build 4447390847:	0.0001%
Covered Lines:	193
Relevant Lines:	16913

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💛 - Coveralls