Focus the specified tool (of the joint.dia.ToolView type) within this tools view.

When a tool is focused, all other tools within this tools view are hidden and the tool's opacity is changed according to the tool's focusOpacity option. Only one tool can be focused at a time; the focus passes to the last tool within this tools view with which the focusTool function was called.

The effect of this function can be reversed for a single tool by the toolsView.blurTool function. All tools can be unfocused by the toolsView.blurTools function.