Updating GP-VAE, adding load_dict_from_h5, etc.

[WenjieDu]

What does this PR do?

1. fixing GP-VAE should return multiple sampling results #276;
2. adding load_dict_from_h5();
3. adding options lazy_load and torch_n_threads for pypots-cli tuning;
4. checking the shapes of inputs in error calculation functions;

Before submitting

• This PR is made to fix a typo or improve the docs (you can dismiss the other checks if this is the case).
• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• I have commented my code, particularly in hard-to-understand areas.
• I have written necessary tests and already run them locally.