Added replace parameter for setText

Requires https://github.com/admc/wd/pull/333 to be pulled first.

I also want to create a test for this in keyboard-specs.js but I can add that in another pull. 

Tested with the wd.js change and it works for me.
I guess it's converting the value array to a string. I agree comments would help.

> Very few source code comments
>appium is written mostly in JavaScript.
>
>Across all JavaScript projects on Open Hub, 21% of all source code lines are comments. For appium, this figure is only 3%.
>
>This lack of comments puts appium among the lowest 10% of all JavaScript projects on Open Hub.
>
>A high number of comments might indicate that the code is well-documented and organized, and could be a sign of a helpful and disciplined development team.
>
> https://www.openhub.net/p/appium/factoids#FactoidCommentsVeryLow