Add zoom controls

[perry]

                    svg.zoomIn = function () {
                        svg.panZoom.zoomIn();
                    };

                    svg.zoomOut = function () {
                        svg.panZoom.zoomOut();
                    };

                    svg.reset = function () {
                        svg.panZoom.reset();
                    };

            <div class="btn-group-vertical log-controls" role="group">
                <button class="btn btn-default" ng-click="svg.reset()">
                    <span class="glyphicon glyphicon-resize-full"></span>
                </button>
                <button class="btn btn-default" ng-click="svg.zoomIn()">
                    <span class="glyphicon glyphicon-zoom-in"></span>
                </button>
                <button class="btn btn-default" ng-click="svg.zoomOut()">
                    <span class="glyphicon glyphicon-zoom-out"></span>
                </button>
            </div>

[perry]

I think the reset can replace your centre method.

[ggdhines-zz]

Need to include a statement in the tutorial about to do this.