Expectations for Obs Shaping?

I just checked the PPO init and saw that only vector-shaped obs are supported (no images) due to only passing obs_shape[0] to buffer and model (same for action). The model creation supports both in principle, so I'm a bit surprised and not sure if this is a good way of handling it since it prevents the use of e.g. Conv Nets for images.

Suggested fix:

- [ ] check SAC and DQN init for the same issue
- [ ] simply pass full obs & action shapes without the index
- [ ] in model init: don't convert to int, simply pass on the raw obs shape