Display a list of activities in the contacts

[edurenye]

We should add a list of activities that this issue participates in, so we can find them easily.

[mirodietiker]

Note that it is very important that we don't do any assumption or add complexity for presentation in th non-UI module.

For now, i would like to have them added as an Activities tab on the Contact. In the long run we need to figure out how we can better decouple the UI appearance and if we are going to use something like page manager with contexts to build the base UI so it is 100% customisable.