(Meta issue) Improve sample load times

[SaschaWillems]

Doing a full batch run in debug mode can take up to 20 minutes. This is especially cumbersome for maintainers, as doing a batch run is now a requirement when doing changes to the framework. One culprit are assets that store textures in ASTC format. This is only supported on mobile and on desktop (where samples are actually developed) those samples need to transcode those textures. This can take a long time, and for a batch run this is done for each and every sample that uses those assets.

We should improve load times of the samples, esp. the ones that use complex scenes.

Related:

• Store Assets in Raw and Compressed formats #860

[SaschaWillems]

Just came up on our reddit: https://www.reddit.com/r/vulkan/comments/1ghalw9/vulkan_samples_slow_loading/