Refactor plotting code, support Brillouin.jl

[kbarros]

Refactors the Plotting module into multiple files.

Resolves #248 by integrating with Brillouin.jl package.

Includes a function view_qspace for visualizing the Brillouin zone, its high-symmetry $q$-points, and other $q$-space objects. This replaces private function viz_qqq_path. The visualization example in #310 becomes:

cryst = Sunny.hexagonal_crystal(; a=1, c=1)
path = q_space_path(cryst, [[0,0,0], [0,1,0]], 14)
params1 = Sunny.specify_transverse_binning(path, [1,1,0], [0,0,1], 0.2, 0.3)
view_qspace(cryst, params1)