Show some stats about the class usage

[stof]

On the page of a class/interface, it would be great to see some stats about its usage:

• number of classes implementing it (this can already be counted manually as they are all listed on the page, but it would be convenient to let the program count for us)
• number of packages containing implementations of the interface (some packages could be providing several implementations, making it even more painful to count it manually from the info displayed on the page)
• number of classes using it
• number of packages using it

all these information are already available by counting things in the current displayed info, so it should not be a huge work to provide a summary. And it would make it easier to have an idea about the usage of a class (especially when a class is used a lot).

[moufmouf]

Yep, good idea, I'll work on that.
Actually, I just realized we could even offer badges for classes :)

Also, on a side note, you should know that we experienced a failure on the server a week ago. The data is currently being loaded again in packanalyst, but some classes are still missing (for instance Symfony packages have not been scanned yet...)

[stof]

@moufmouf an improvement would be to add a banner on the website with a warning saying that dara are incomplete when such thing happens.