A couple of tweaks for up to 40% faster PDE start-up

I was taking a look at the start up process of the PDE and found a couple of bottlenecks that occur due to file I/O. After eliminating them, on my setup, (Ubuntu 12.10 x64, no SSD) the average start up time decreased from ~1900ms to ~1170ms. An improvement of nearly 40%.

I found these culprits:
* Base.getSketchbookMenu(), which when invoked for the first time, populates the menu and then returns the JMenu. The file I/O in the first function call was taking ~500ms with my sketchbook. This method is first called in the Editor class constructor. I modified this function to immediately return a blank JMenu, so that the Editor loads up quickly via the main thread. The sketchbook JMenu, in the meanwhile, is populated in the background by a separate thread without blocking the main thread from loading the Editor. This shaved off ~500 ms from the start up time. I added a new getSketchbookMenuFast() method. 

* Editor.getToolMenu() - A similar case as the above, where JMenu takes time to be populated when done in the main thread. Following similar approach as above, I lazy load this menu in the background. This saved another ~200ms. I added a  getToolMenuFast() method.