- Remove the `plugins.remove` API method.
- Throw an error when attempting to register multiple plugins with the same name.

updates #752

To illustrate that this is not necessary (and also not possible with
non-bundled plugins).

to indicate that it's private and to differentiate it from the outer "global"
converse object.

Specifically involving querying by the 'xmlns' attribute, where I've had issues
in the past.

after allowing chatting with pending/requesting contacts

Also add `/subject` as alias to `/topic`

Attempt reconnection on authfail when credentials_url and auto_reconnect are set.

Let debounced reconnection happen on the leading edge.

Also update pluggable.js to a version that works with lodash.

- Add a test case.
- Don't allow passing of `attrs` to `chats.open`. Not sure yet of the
  implications of this.

Resolves #760.

https://greenkeeper.io/