Fix webmachine_demo with refactored ensure_all_started function

We have a special version of ensure_all_started that uses the default Erlang implementation if it's available, and otherwise falls back to our own reimplemented version of the function. I made some minor changes and factored this out into the webmachine_util module.

This function is then used in webmachine_demo to fix a startup crash that was occurring due to ssl not being started.

This PR is basically an expanded, completed version of #219 using the changes suggested by @vinoski