Show JS parameter hint

Implements a new command, "Show Parameter Hint".
Shows the parameters of a function and bolds the hint where the cursor is located. Automatically shows a parameter  hint when a function is selection from the code hints dialog.

Current limitations:
    1. no automatic parameter hint for selected hints that are "guesses".
    2. no hint of record type annotations (Tern issue [#207](https://github.com/marijnh/tern/issues/207))
    3. problem with optionals hints (fixed in latest Tern, issue [#208](https://github.com/marijnh/tern/issues/208))
    4. Array.<string> annotation shown as Array.<Object> (needs investigation).