Clean stage again

[maxtremblay]

• Uniformize many names and clarify some short (or wrong) names.
  • Use tile_count with either the m, n and k axes or the row and col axes
    for the number of tiles within a stage.
  • Use tile_shape for the shape of a tile.
  • Use tile_size for the total number of elements in a tile. The product of all shape of a time.
• Introduce a new concept of StageTiling that replace many previously used traits and structs related to tiling. A CompleteStageTiling is able to work with both the mnk axes and the row-col axes.
• Remove a few now unused traits, structs and functions.

[laggui]

LGTM!

Missed a docstring, but approving in advance.