Minor fixes for carbons

I've found a problem, some messages didn't have to or from fields, that made it hard for the client to understand where the message came from.

F.e. clientA sends mesage to clientB:
```
<message to="clientB">
</message>
```
Then clientB receives a carbon:
```
<message to="clientB">
</message>
```
And it's hard to determine who sent the message to him.