[WIP] Follow Users feature

[aajjbb]

Adding the ability to follows Users (and not only modules).

• It's a work in progress because I can't automatically test because of #109
• I found it weird that the URI for an users profile is /modules/:username. Wouldn't call it /users/:username better ?

[leafo]

I found it weird that the URI for an users profile is /modules/:username. Wouldn't call it /users/:username better ?

It's a little weird but it's fine to leave it for now. If we want to change it in the future then we'll need to make sure to use a redirect.

[leafo]

Thanks!