WebDriver test for executing react editor through "Alpha" button

Test that the React editor shows, with appropriate textflows displayed

Notes:
Currently react editor does not work in functional test due to context path issue. https://zanata.atlassian.net/browse/ZNTA-1790
Prerequisites for this is to deploy Zanata as ROOT context in functional test, and allow browsing of the react editor in functional test.
The context path should be configurable via maven variables but default to root `/` by default.