Issues/95 get user affiliations

This removes all instances of database methods for:

- get node subscriptions
- get user subscriptions
- get node affiliations
- get user affiliations

It also removes RSM from subscriptions and affiliations get methods - this adds too much complication for supporting mega groups.

If we consider:

```
<subscription subscription="subscribed" node="/user/my-super-long-channel-name@topics.buddycloud.org/posts" />
```

You are talking ~800 subscriptions before we begin to reach the stanza limits (similar for affiliations, although this number will change due to multibyte characters and length of node name, etc).

...and this of course assumes that 64kB limit is being monitored strictly in the XMPP server.

If needed we can add this back in, but I'd prefer to keep the server code more simple for now.

Fixes #95
Closes #179