Add dihedral angle functionality

[billera]

• Compute dihedral angles

• Map dihedral angles with corresponding bond lengths and angles to xyz coordinates

• Idealize the bond lengths and angles of existing structures while maintaining similarity to the original structure.

[AntonOresten]

I have no idea how pull requests, forks, and remotes work so I just created #9 with some tweaks and merged that into main.

Changes:

• Access the batched_mul function through NNlib instead of Flux to avoid unnecessary indirect dependencies
• Rename backbone/distance.jl to backbone/bonds.jl
• Use backbone_bond_vectors function in backbone/bonds.jl
• Add tests for idealized bond length functions (tests still missing for some functions)
• Rename global bond_lengths and bond_angles variables to MEAN_BOND_LENGTH and MEAN_BOND_ANGLE turn into consts.
• Remove module Dihedrals with hopes of making the functions work well with the Backbone type
• Turn bond_lengths and bond_angles into keyword arguments
• Rename get_triangle to law_of_cosines
• Add ::Backbone method to get_dihedrals function

All this helped me realize that oxygen atoms shouldn't be part of the backbone, and we can probably leave that to the Chain type, see #10.