Not suppported features, proper workarounds

[haraldsteinlechner]

• multidraw crashes with segfault if not supported
• textureviews?
• fbos with unsupported sample count may segfault - high level get sample count function needed here.

[hyazinthh]

Sample count issues should be resolved.

[hyazinthh]

Creating texture views fails with a proper exception. Best thing is to not use them, the Vulkan backend will probably never support them with the current API.