Python-testui

* Add element `clear()` method
* Fixes for image comparison
* Fix for TestUI element creation

Possibility to add a custom driver to the TestUI driver

driver = NewDriver() \
.set_logger().set_driver(custom_driver)

Small Patch:
1. Fix for locally created chromedriver to add chrome options
2. Remove extra logging when remote selenium is not used

Firefox to use marionette as default
Firefox automatic geckodriver download
improve Readme
Remove default screenshot directory

- Fix for Circular import
- Fix for absolute and relative app path

- Fix for Attribute text
- NewDriver() setter methods (set_screenshot_path(), set_save_screenshot_on_fail(), set_save_full_stacktrace())
- driver:TestUIDriver instance properties (driver.configuration.screenshot_path, driver.configuration.save_screenshot_on_fail, - - driver.configuration.save_full_stacktrace)