* Bug fix for eye tracking in HMD, the "up" orientation of your eyes now match your head.
* DebugDraw: added drawRay method.
* Application: Renamed preRender to postUpdate
* AvatarManager: added postUpdate method that iterates over all avatars.
* MyAvatar: Renamed preRender to preDisplaySide
* MyAvatar: split preRender code into postUpdate and preDisplaySide.
* Removed "Show who is looking at me", "Render focus indicator" and "Render lookat target" debug draw.
* Split "Show Look At Vectors" into "Show My Look At Vectors" and "Show Other Look At Vectors", to make it easier to debug eye tracking.
* "Show Look at Vectors" now draws the right eye red and the left eye blue.
* Removed Avatar and MyAvatar renderBody
* Removed look at rendering from head.
* GLMHelpers: Bugfix for generateBasisVectors when up primary and secondary axis were orthogonal
* Prevent clusterMatrices from being invalidated and re-computed in each updateItem lambda.
We do this by not setting _model->_needsUpdateClusterMatrices = true;
* Prevent redundant work if Model::enqueueLocationChange is called multiple times per frame.
We do this by introducing a preRenderLambdas map in the Application class.
Instead of adding work directly to the scene PendingChanges queue Model::enqueueLocationChange
adds a lambda to the Application preRenderLambdas map. The Application ensures that only one lambda will
be invoked for each model per frame.
