Visualtest-python

- Improved Safari screenshots
- Add method for getTestRunResult

What's Changed
* Changed debug settings - only `debug=true` will save logs and images to disk under `sbvt_debug` folder
* No files are written to disk by default unless `saveTo` or `debug` setting is provided (allows to run where I/O is unavailable)
* All images are built and managed in memory before being saved via the API
* Removed automatic printing of results to console
* Added `printReport` instance method for printing results to screen after a test run
* Add `comparisonMode` option to capture method to override default project setting

* Fix ignoredElements bug not clearing each capture

* Fix viewport bug

* Run `freezePage` script by default with opt-out setting
* Added new `chrome-os-version.js` script for getting proper osVersion
* Handle `lazyload` and `ignoreElement` validation in fullpage test cases

- Added `ignoreElements` option to capture method