Fix save deg p

[keiyamamo]

Fix #61

Combination of the degree that I tested

1. d_deg = v_deg = p_deg = save_deg = 1
2. d_deg = v_deg = 2, p_deg = 1, save_deg = 1
3. d_deg = v_deg = 2, p_deg = 1, save_deg = 2

I tried to test higher order elements like P3P3P2 but Newton solver diverged on my laptop.

[keiyamamo]

Tested against

1. d_deg = v_deg = p_deg = save_deg = 1
2. d_deg = v_deg = 2, p_deg = save_deg = 1
3. d_deg = v_deg = 2, p_deg = 1, save_deg = 2
4. d_deg = v_deg = p_deg = save_deg = 2

and confirmed that all visualization looked as it should. I decided to add a check that raise an error when save_deg is larger than the v_deg. I will merge now but please feel free to ask questions or give me feedback.