Dependencies: improve redaing and navigation

[Chris00]

When a package has many dependencies, such as http://opam.ocamlpro.com/pkg/jenga.109.18.00.html, it would be nice if they were listed in a clearer way. It would also be nice if they were links.

This is what is actually done to the right and it is a duplicate of information. If think the two should be merged (also for optional deps) and the right column should only be used for "side information" such as

1. reverse dependencies (as of now);
2. suggestions of similar packages (e.g. using tags);
3. packages in the same categories, e.g. "scientific", "graphics",... (again using tags but picked up in a given list).

[dsheets]

I've made everything a link and translated the formulae structure into DOM structure.

If you could elucidate your tag ideas in other issues, that would be great.

Better reverse dependency support (with consolidated ranges) will arrive soon with the fix to #78.