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.
Is that any chance that the "replace" param will be missing?  If so, you should handle that scenario. Eg,

bool replace = false;
if(params.get("replace") != null) {
// now parse
}

If you know  that replace will always exist, then no worries.