Add tag for friends in the internal friendlist

[jmderuty]

It's currently impossible to differentiate a friend who is in both in the internal friendlist & a platform friendlist vs a friend who is only a platform friendlist.

We should add a tag named platform:stormancer to all friends records (invitations/friends/blocked) in the internal friendlist so that they can be identified as such by game clients to allow, for instance, players to remove them from their internal friendlist.

[jmderuty]

We should also check Platform plugins to make sure they use the same platform:xxx tag format to advertise that social records are present in their managed friend list.

[Falanwe]

EOS plugin has been updated to use platform:eos as a platform tag