Fix terrain lighting

[Schneegans]

Changes:

• Added a new ambientOcclusion setting which for now controls the amount of artificial hill-shading on the terrain. Previously, this was hard-coded.
• Reduced some code duplication in the planet shader.
• The tile-borders of csp-lod-bodies can now also be visualized in HDR mode.
• Ambient lighting works again in HDR-mode,
• Ambient lighting is set to a more realistic value of zero per default.
• The mapping of the ambient-lighting slider now feels more linear (both in HDR and non-HDR mode).
• If ambient lighting is set to one, the terrain is not affect by the sun light direction anymore.
• The ambient lighting now properly interacts with eclipse shadows on simple bodies.

[coveralls]

Pull Request Test Coverage Report for Build 4354113969

• 0 of 15 (0.0%) changed or added relevant lines in 4 files are covered.
• 100 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.002%) to 3.107%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/csp-lod-bodies/src/PlanetShader.cpp	0	2	0.0%
plugins/csp-lod-bodies/src/TileRenderer.cpp	0	2	0.0%
src/cs-core/Settings.cpp	0	2	0.0%
src/cosmoscout/Application.cpp	0	9	0.0%
<!--	Total:	0	15	0.0%	-->

Files with Coverage Reduction	New Missed Lines	%
plugins/csp-lod-bodies/src/TileRenderer.cpp	2	0%
plugins/csp-lod-bodies/src/TileSourceWebMapService.cpp	98	0%
<!--	Total:	100		-->

Totals
Change from base Build 4204689113:	-0.002%
Covered Lines:	515
Relevant Lines:	16578

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💛 - Coveralls