Navigational mesh - analyze cells to check for computational shortcuts

[Garanas]

We now collect information while we pre-analyze a cell. This allows us to make better decisions to just flatten a cell. As an example: there is no need to analyze a cell for land capabilities when it entirely consists of water. This saves roughly 5% to 10% on the computation time. It has less of an impact on larger maps as the dominant factor on larger maps is the raw quantity of heightmap samples.

Old situation:

Alpha Quarantine:
DEBUG: NavGenerator - culled 424 labels
DEBUG: Generated navigational mesh in 5.720215 seconds
DEBUG: Allocated megabytes for navigational mesh: 24.007584
DEBUG: Allocated megabytes for labels: 0.198051

Seton's Clutch - FAF version:
DEBUG: NavGenerator - culled 197 labels
DEBUG: Generated navigational mesh in 2.016846 seconds
DEBUG: Allocated megabytes for navigational mesh: 15.915611
DEBUG: Allocated megabytes for labels: 0.141205

Open Palms - FAF version:
DEBUG: NavGenerator - culled 102 labels
DEBUG: Hover grid equals land grid - ditching hover grid
DEBUG: Amphibious grid equals land grid - ditching amphibious grid
DEBUG: Generated navigational mesh in 1.137451 seconds
DEBUG: Allocated megabytes for navigational mesh: 4.909599
DEBUG: Allocated megabytes for labels: 0.080338

New situation:

Alpha Quarantine:
DEBUG: NavGenerator - Flattened 374 sections
DEBUG: NavGenerator - culled 424 labels
DEBUG: Generated navigational mesh in 5.545898 seconds
DEBUG: Allocated megabytes for navigational mesh: 24.007584
DEBUG: Allocated megabytes for labels: 0.198051

Seton's Clutch - FAF version:
DEBUG: NavGenerator - Flattened 414 sections
DEBUG: NavGenerator - culled 197 labels
DEBUG: Generated navigational mesh in 1.924316 seconds
DEBUG: Allocated megabytes for navigational mesh: 15.915611
DEBUG: Allocated megabytes for labels: 0.141205

Open Palms - FAF version:
DEBUG: NavGenerator - Flattened 908 sections
DEBUG: NavGenerator - culled 102 labels
DEBUG: Hover grid equals land grid - ditching hover grid
DEBUG: Amphibious grid equals land grid - ditching amphibious grid
DEBUG: Generated navigational mesh in 1.056396 seconds
DEBUG: Allocated megabytes for navigational mesh: 4.909599
DEBUG: Allocated megabytes for labels: 0.080338