- all vulkan data unique for application are managed by
  VulkanGlobalState that is stored in Application
- VulkanState contains data unique for WindowContext and reference to
  VulkanGlobalState
- pipeline and validation (shader) caches are supported
- helper utilities: on_scope_exit/failure and CacheFile (simple mappeed
  file)

- WindowContext renamed into RenderContext
- style refactoring
- width & height are replaced with Extent

- refactor vulkan handles initialization with vk-bootstrap
- some minor refactoring