BGE : Collision mask support in raycast + and raycast cleanup.

I have removed the m_pHitObject, m_xray and m_testPropName and replace them by a temporary struct "RayCastData" which contains these datas and a collision mask. Finally i add a collision mask argument in the python function "rayCast" :
```
rayCast(to, from, dist, prop, face, xray, poly, mask)
```

It can be useful to hit only object which are on the right colision layer. for example if you have hitbox for a charater or vehicle you don't want to hit it with raycast.

test file : {F237337}
left mouse click on two planes and see console messages.

Somewhat more elaborate test file by @sybren: {F237779}
Look around and click on the cubes. One cube lamp responds, the other doesn't, based on their collision groups.

Reviewers: moguri, hg1, agoose77, campbellbarton, sybren

Reviewed By: agoose77, campbellbarton, sybren

Subscribers: campbellbarton, sergey, blueprintrandom, sybren

Projects: #game_engine, #game_physics

Differential Revision: https://developer.blender.org/D1239

doc/python_api/rst/bge_types/bge.types.KX_GameObject.rst

@@ -799,7 +799,7 @@ base class --- :class:`SCA_IObject`
       :return: the first object hit or None if no object or object does not match prop
       :rtype: :class:`KX_GameObject`
 
-   .. method:: rayCast(objto, objfrom, dist, prop, face, xray, poly)
+   .. method:: rayCast(objto, objfrom, dist, prop, face, xray, poly, mask)
 
       Look from a point/object to another point/object and find first object hit within dist that matches prop.
       if poly is 0, returns a 3-tuple with object reference, hit point and hit normal or (None, None, None) if no hit.
@@ -851,6 +851,8 @@ base class --- :class:`SCA_IObject`
          * 2: return value is a 5-tuple and the 5th element is a 2-tuple (u, v) with the UV mapping of the hit point or None if no hit, or the object doesn't use a mesh collision shape, or doesn't have a UV mapping.
 
       :type poly: integer
+      :arg mask: collision mask: The collision mask (16 layers mapped to a 16-bit integer) is combined with each object's collision group, to hit only a subset of the objects in the scene. Only those objects for which ``collisionGroup & mask`` is true can be hit.
+      :type mask: bitfield
       :return: (object, hitpoint, hitnormal) or (object, hitpoint, hitnormal, polygon) or (object, hitpoint, hitnormal, polygon, hituv).
 
          * object, hitpoint and hitnormal are None if no hit.