factor out 'webglcontextlost' listener

[pixelzoom]

3/9/17 dev meeting:

Molecule Shapes (phetsims/molecule-shapes#147) and Neuron (phetsims/neuron#134) contain duplicate code for handling WebGL context loss.

MoleculeShapes.MoleculeShapesScreenView:

      this.threeRenderer.context.canvas.addEventListener( 'webglcontextlost', function( event ) {
        event.preventDefault();

        self.showContextLossDialog();

        if ( document.domain === 'phet.colorado.edu' ) {
          window._gaq && window._gaq.push( [ '_trackEvent', 'WebGL Context Loss', 'molecule-shapes ' + phet.joist.sim.version, document.URL ] );
        }
      } );

Neuron.ParticlesWebGLNode:

    this.contextLossListener = function( event ) {
      event.preventDefault();

      new ContextLossFailureDialog().show();

      if ( document.domain === 'phet.colorado.edu' ) {
        window._gaq && window._gaq.push( [ '_trackEvent', 'WebGL Context Loss', 'neuron' + phet.joist.sim.version, document.URL ] );
      }
    };

    // set up a handler for context loss - this will just put up a dialog, better handling may exist eventually
    gl.canvas.addEventListener( 'webglcontextlost', this.contextLossListener );

This code should be factored out. @jonathanolson volunteered to handle this, and determine the appropriate place for it.

[pixelzoom]

This is also related to phetsims/joist#411. The usage of phet.joist.sim.version should be replaced with whatever abstraction is provided for the version identifier.