Add support for scope in has-one association

[verdier]

This PR fix two issues:

• the association's scope was not injected in where clause when eager loaded. This is extremely critical because any raw that match without the where restriction is eager loaded, that could result in sending private data to the client (that's what append to us...),
• the association's scope was not used is the creator helper method (ie. createInstance)

[mickhansen]

hasOne never had scope support, soooo ;p
The two bugs you mention are actually just the fact that the implementation does not exist.

[verdier]

Haha @mickhansen that's fun... the implementation is here. Could you merge?

[mickhansen]

Needs code and test for associationGetter aswell.

[verdier]

Ok I'll do that tomorrow

[mickhansen]

Great, will merge then :)

[verdier]

@mickhansen done. Ready to be merged.