Refactor observations

[Lj Miranda]

I think it's better for our observation space to be a grid rather than a chain:

• Create a matrix of shape (m, m) matrix where m = 2 * len(seq) + 1
• Get the midpoint of that grid and treat that as origin. That's why you want to have odd number of cells
• The grid should have values in {-1, 0, 1} for polar, unassigned, and hydrophobic separately