Moved xpath into boostrap java

And removed complex-find while at it.

Submitting to @bootstraponline for review.

I'm working now on changing the getPageSource code to reuse the same code here.
I think appium needs a high level design doc which explains some of these technical decisions. Then when new devs start working on the project, the on boarding is easier.

https://github.com/appium/appium/issues/3431