On package detail page add 'similar to' section

[pydanny]

Add the set of all packages in all grids that contain a particular package

[ryancheley]

I think that this is already covered by the Comparison Grids section. This section lists out the Grids which are hyper linked to the grids page which shows all of the packages. I'm not sure that listing all of the related packages would add value to the page and might just make it harder to use