Add Android support

[SaschaWillems]

Android is one of Vulkan's most important target platforms, yet the tutorial only works on and talks about desktop platforms. Android support should be added both to the tutorial as well as the code. We probably can leverage the Android stuff we use in our samples.

[charles-lunarg]

Thinking about this, there are a few open questions as well as distinct work items:

• GLFW doesn't support Android, so some android specific windowing & input code would be required. (Taking from Vulkan-Samples is fine for this)
• The appropriate 'development environment setup' for android would need to be included as well.
• Enabling validation layers is the same on all platforms, but getting validation layers into an application on android is not, so that would need to be covered.

[SaschaWillems]

Will be fixed by #80