SoundPicker indicator icon hotfix, Sphere API menu item

When you moved the imagelist off the form into the code, you forgot to set the indexer keys, took me a minute to figure out why the icons didn't work anymore.

I also added a Help menu item for the Sphere API docs which routes through OpenDocument() so that the file opens right in the IDE in whichever plugin happens to handle .txt files.  I got tired of hunting for the api.txt all the time while developing Spectacles. ;)