Don't use patches which lie outside the bbox of the brushes during navmesh generation

This improves navigation mesh generation for StarAtcs.
The resulting navigation mesh is much smaller and accuracy is much higher.
Simplify the contents check for brushes during navmesh generation

checking for CONTENTS_BODY does not make sense because it is exclusively used for entities added in game.
Increase the tile border size

This allows rcFilterGaps to work across tile boundaries