add support to select the parent frame

[DinisCruz]

At the moment it is only possible to 'navigate into' a particular frame (using https://github.com/admc/wd/blob/1038c33b0abbe8329d81c9bb6bb62e3df3b440fa/lib/commands.js#L327) As per the JsonWireProtocol specification, there is a /frame/parent method that can be called.

Here is how I got it to work on my test script

resetToParentFrame = function() 
   {
       browser._jsonWireCall(
            {
                method: 'POST' , 
                relPath: '/frame/parent' , 
                data: {} , 
                cb: viewData
            }) 
   }

It would be nice to add this as an officially supported wd method

[mrak]

:+1:

[sebv]

Just add it to command.js and open a PR.