Streamline packing density computation;

See merge request sapme1/hexagonalsampling!2

Make new plot for example grids;
Add yellow blip-up-down line in grids;
Plot blipped CAIPIRINHA & Narsude separately in DvsR plot;
Decrease y range in grid plots;
Add units to grid plot;
Change slab border colour from red to light blue;
Plot all L's (<=N) not only the ones that make sense (for demonstration)

Initial commit

See merge request sapme1/hexagonalsampling!1