UI-Core separation refactoring

This commit performs separation of the UI and Core parts of the
application.
Resolves #7.

- New Core component is introduced. It implements the main logic behind
the UI.
- IView represents a view in the Core component.
- Startup logic in Holo.UI is simplified.
- HoloKernel is renamed to Holo.Core.
- Target platform is restricted to x86 to allow BASS libraries work by
default.