You can use layouts created in the plug-in manager. They're available from the Plug-Ins drop-down menu.
Please consider reading the
eZine that accompanies each new release that describes how the new features work. For example, you can do things like use the new features in the Browser to populate the plug-in manager with a new, categorized default plug-in layout.
The bottom line is you haven't lost anything, and gained lots of options that weren't available before.
As to whose idea it was to categorize plug-ins, blame Steinberg

. They came up with the VST3 spec. However SONAR lets you modify the categorization, so you have the best of both worlds.