Started work on a more general positional index.
Merge branch 'master' into new_space_index
Merge branch 'master' into new_space_index

Conflicts:
	src/core/simulator/space/space_hash.h

Compilation is still broken.
Created a directory for the space positional indices and moved everything in.
More work on the grid positional index. Plugins removed from compilation. Testing started but not finished.
Finished grid-based index. Tested, it works. Plugins are still not compiled, and the positional index is not integrated yet.
Towards the grid for embodied entities.
Merge branch 'master' into new_space_index
Restored compilation with the positional index in place for the embodied entities.

TODO:
- Implementation of the GetClosestEmbodiedEntityIntersectedByRay(), in two variants;
- RAB default sensor is out of compilation;
Now the GetClosestEmbodiedEntityIntersectedByRay() function ignores only one embodied entity. The version that ignored a list of entities was never used, and this change allows for a much faster implementation.
Added implementations for the intersection of embodied entities. Still to be tested.

TODO: right now it uses the method CPositionalIndex::ForEntitiesAlongRay(), stopping at the first match. This is not strictly correct, because multiple entities could be present in a grid cell.
Fixed implementation of the embodied entity ray intersection check. Untested, but it should provide all the necessary features.
Tested new grid with embodied entities, it seems to work pretty nicely.
New text XML.
A few fixes for the grid of embodied entities, which now works nicely.
Added the SinCos function in angles.h, that calculates sine and cosine at the same time. Used in quaternion and vector classes.
Used RTLD_LAZY instead of RTLD_NOW.
Fixed the compilation of testing material.
Fixes to the test experiments
Huge commit.

Added a new type of plug-in, the media. It is meant to support the simulation of communication among robots, and other stuff.

TODO
- Multi-thread computation not supported yet