Implement basic functional tests for UI

Our UI has only-web.rb and hooks.js specifically to facilitate automatic isolated testing of UI. I.e. testing of UI without server-side components.

We even have a couple of outdated cucumber tests utilizing that facilities. See deps/menelaus/priv/ruby/cucumber.

Goal of this tech story is to (re)implement basic framework for running such tests and covering most basic UI features. This story needs to include both framework development and initial coverage because we need some real framework usage to guide framework development.

I suggest covering the following:

• basic navigation (switching sections works and doesn't raise any exceptions)
• setup wizard (all cases work and issue right POST requests)

This goals will ensure that we have all facilities in place for testing of UI.