Revisit and refactor create_image_from_file implementation

[johannesugb]

The implementations of gvk::create_image_from_file are somewhat strange. Depending on the input format, either gli or stbi is used to load the image.

Review the way these methods are implemented and possibly refactor them. Maybe even come up with an interface that makes more sense (e.g. inferring the format completely automatically instead of passing the desired format to the create_image_from_file(const std::string& aPath, vk::Format aFormat, avk::memory_usage aMemoryUsage = avk::memory_usage::device, avk::image_usage aImageUsage = avk::image_usage::general_texture, avk::sync aSyncHandler = avk::sync::wait_idle()) overload).

It would make sense to work on this issue in conjunction with working on issue #59.

Definition of done:

• Implementations of gvk::create_image_from_file functions have been evaluated and improved in terms of readability, functionality, and code-reuse.
• The implementation is less confusing than in the current state --- or at least better documented.
• gvk::create_image_from_file functions are well documented and the Contribution Guidelines have been followed.