* account for availability of next level in desired level
solves #2834
* remove tile-padding option & functionality
* remove (no longer needed) recursive read function
since we no longer padd tiles we cannot sample outside of a read region
anymore.
* change default tilesize for heightlayers to avoid discontinuities
* make frustum culling control a debug property
* Small style guide fix
* clarify if-statement with comment
* add variable for default height-tile resolution, update comment
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Co-authored-by: Alexander Bock <mail@alexanderbock.eu>