Introducing a Detour NavMesh creator helper library

This new library facilitates the creation of navmeshes for Detour. At the moment it only supports the creation of Tiled NavMesh where all tiles uses the same configuration.

It is now used by `DetourCrowdTest` and `DetourCrowdDemo`. The goal is to also use it in `RecastDemo` to unify all navmesh creation helpers and hopefully facilitate first contacts with Recast/Detour. The changes in `DetourCrowdDemo` also have the nice side effect of reducing the test time by a **huge** margin as the computed navmesh are kept between tests.

**Further improvements**
- Fixed an aliasing problem when doing `crowd.addAgent(ag, ag.position)`.
- The file format used by `DetourCrowdDemo` now allows the sharing of behaviors between agents.
- A new `DetourCrowdDemo` sample now showcases the avoidance of non-moving agents.
- In files otherwise modified, existing *space* indents have been changed to *tab* indents.