Removed completed TODOs.

DG_Approximation.py

@@ -7,16 +7,10 @@ TODO: Contemplate saving 5-CV split and evaluating models separately
 TODO: Contemplate separating cell average and reconstruction calculations
     completely
 TODO: Contemplate removing Methods section from class docstring
-TODO: Ask whether there is a difference between grid and mesh -> Done
-    (same, keep mesh)
 TODO: Contemplate containing the quadrature application for plots in Mesh
 TODO: Contemplate containing coarse mesh generation in Mesh
 
 Urgent:
-TODO: Introduce Mesh class
-    (mesh, cell_len, num_grid_cells, bounds, num_ghost_cells, etc.) -> Done
-TODO: Add property attribute for non-ghost cells in Mesh -> Done
-TODO: Replace mesh with Mesh class -> Done
 TODO: Put basis initialization for plots in function
 TODO: Contain cell length in mesh
 TODO: Contain bounds in mesh