Remove duplicate and declared in parent code: create_web_element
Remove duplicate 'get screenshot as file' methods.

Add method 'get_screenshot_as_png' to allow get screenshot image binary data.

Reuse code with these 3 methods.
Implement test for issue #5069
Limits screenshot at fxdriver by 32767 pixels.

Done:
* add limit 32767 pixels for screenshot sizes
* improve logging at screenshot errors
* update and cleanup TakesScreenshotTest test code
* enable TakesScreenshot for Sauce test driver

Fixes issue 5674.