Fix Social Network Auth

[eluhr]

Q	A
Is bugfix?	yes
New feature?	yes
Breaks BC?	yes/no -> Update in interface but trait to support backward compatibility
Tests pass?	yes
Fixed issues	https://github.com/2amigos/yii2-usuario/issues/359, https://github.com/2amigos/yii2-usuario/issues/383

While I was trying to use the social account feature of the module, I noticed that the feature is not implemented properly in some places or does not work at all in some scenarios.

• When attempting to log in for the first time via an unconnected network account, the user model is not saved in the database.
• The SocialNetworkServices require an "id" field in the received data packet. More flexibility is provided by adapting the interface and providing a trait for backwards compatibility.
• New property that allows login exclusively via social networks, regardless of the value of the "enableRegistration" property.
• New property that allows you to prevent the sending of a "welcome message" when the user registers via a social network.

This PR solves these problems and at the same time provides a little more flexibility in use.

[maxxer]

Wow, thank you for the work! Please add an entry to the changelog then I'll merge it.

[eluhr]

@maxxer thx! i just updated the changelog.