Import code from ru.org.codingteam.keter.ui

[ForNeVeR]

ru.org.codingteam.keter.ui package should become a basis for the Euclid code.

• [x] import the main code and make sure it compiles
• [x] import the Scene stuff
• [x] add some simple examples to make sure it works at least partially
• [ ] add some simple tests
• [ ] review the platform abstraction layer
• [ ] add the documentation

[ForNeVeR]

The code has been imported. I've created separate issues for some of the tasks, and we'll require to add the unit tests with every new pull request.