adding async and fs-extra to help with installation tasks
handles basic installation
installation handles the case of extensions that are already
installed (installing into disabled in those cases)
removes the requirement for a package.json
wired installation through to the client
remove test that is no longer relevant (package.json can be missing
legally, and the test that follows the deleted one catches validation
issues in general)
Merge in the almost done (still needs comments and client side tests) extension installation code