Migrate to SeleniumHQ 3

[cezarypiatek]

1. Update nuget package to Selenium 3
2. Update script for downloading webdrivers (add geckodriver)

[kmorcinek]

ad 1. I can update them. When will I be sure that everything works? When the code compiles and the SampleUITest tests are passing?

ad 2. Should it be done similar to #20 ?

[kmorcinek]

I have created a bug #21 that covers updating to geckodriver. The are separate think (geckodriver and Selenium 3), so separate issues are better, @cezarypiatek what do you think?

[cezarypiatek]

Ad1. I have a private set of tests (over a 300 assertions) When I run this suit and everything will be ok then I'll accept your PR.

Ad2. Please extend script for downloading drivers. Nuget packages should be an alternative (there is no OFFICIAL nuget package with given driver)

[cezarypiatek]

According do geckodriver issue tracker (https://github.com/mozilla/geckodriver/issues) there is a lot issues related to clicking and typing (SenKeys) so I'm still not convinced about migration to Selenium 3.X

[kmorcinek]

I fully understand that.

[cezarypiatek]

I've created branch SeleniumHQ_3_5 with Selenium 3.6. There has been introduced two BrowserTypes related to Firefox:

1. BrowserType.Firefox -> Use legacy Firefox Driver for Firefox 47.0.1
2. BrowserType.FirefoxGecko -> Use Geckodriver (marionette)

This is necessary because Geckodriver has issues with clicking what makes impossible to create stable UI tests. It also does not support full page screenshots what makes VisualAssertion useless.