auto-configure Product Name

You know how we tell plug-in devs to remove all the bold build settings except “Product Name”? I don’t think that’s necessary. If we set `PRODUCT_NAME` to `TARGET_NAME`, all the plug-ins can get a reasonable value automatically (and we can just tell people to delete all the bold settings).

I’ve also:

  * Removed the hard-coded product name from all the built-in plug-ins
  * For the targets that aren’t plug-ins, but the product name is the same as the target name, I’ve removed the hard-coded product name and replaced it with `$(TARGET_NAME)`
  * Changed the Finder plug-in’s target from “Finder Module” to “Finder Plugin”