Clean up Convex geometry (bug, documentation, API, and testing)

The Convex class had a bug -- bad computation of local AABB. That was the
springboard that led to numerous changes. They include:

1. Correction of AABB calculation (with supporting unit tests).
2. Overhaul of Convex API
    - removed unused members (plane_normals, plane_dis, and edges)
    - renamed remaining members to be more consistent with mesh description.
    - modification of references to those members.
3. Added extensive doxygen documentation consistent with the new API.
4. Initial unit tests for Convex geometric properties (volume,
   center-of-mass, and inertia tensor).
5. Note issues in the code with TODOs and link to github issues.
6. Update Changelog.md to reflect the change in this PR.

CHANGELOG.md

@@ -13,6 +13,10 @@
   * Switched to Eigen for math operations: [#96](https://github.com/flexible-collision-library/fcl/issues/96), [#150](https://github.com/flexible-collision-library/fcl/pull/150)
   * fcl::Transform defined to be an Isometry to facilitate inverses [#318](https://github.com/flexible-collision-library/fcl/pull/318)
 
+* Geometry
+
+  * Simplified Convex class, deprecating old constructor in favor of simpler, documented constructor: [#325](https://github.com/flexible-collision-library/fcl/pull/325)
+
 * Broadphase
 
   * Fixed redundant pair checking of SpatialHashingCollisionManager: [#156](https://github.com/flexible-collision-library/fcl/pull/156)

include/fcl/geometry/collision_geometry-inl.h

@@ -141,6 +141,13 @@ S CollisionGeometry<S>::computeVolume() const
 template <typename S>
 Matrix3<S> CollisionGeometry<S>::computeMomentofInertiaRelatedToCOM() const
 {
+  // TODO(SeanCurtis-TRI): This is *horribly* inefficient. In complex cases,
+  // this will require computing volume integrals three times. The
+  // CollisionGeometry class should have a single virtual function that will
+  // return all three quantities in one call so that particular sub-classes can
+  // override this to process this answer more efficiently. The default
+  // implementation can be exactly these three calls.
+  // See: https://github.com/flexible-collision-library/fcl/issues/327.
   Matrix3<S> C = computeMomentofInertia();
   Vector3<S> com = computeCOM();
   S V = computeVolume();