Message queue

This is my first pass at message queue support for the CLI.

This relies on issue #100.

**Module Help**
```
usage: sl messaging [<command>] [<args>...] [options]

Manage SoftLayer Message Queue

The available commands are:
  account  List all queue accounts
  queue    Queue-related commands
  topic    Topic-related commands
```

**Queues**
```
usage: sl messaging queue list <account_id> [options]
       sl messaging queue detail <account_id> <queue_name> [options]
       sl messaging queue create <account_id> <queue_name> [options]
       sl messaging queue modify <account_id> <queue_name> [options]
       sl messaging queue delete <account_id> <queue_name> [<message_id>] [options]
       sl messaging queue push <account_id> <queue_name> (<message> | [-]) [options]
       sl messaging queue pop <account_id> <queue_name>  [options]

Manage queues

Queue Create/modify Options:
  --visibility_interval=SECONDS  Time in seconds that messages will re-appear
                                   after being popped
  --expiration=SECONDS           Time in seconds that messages will live
  --tags=TAGS                    Comma-separated list of tags

Queue Delete Options:
  --force  Flag to force the deletion of the queue even when there are messages

Pop Options:
  --count=NUM  Count of messages to pop
```

**Topics**
```
usage: sl messaging topic list <account_id> [options]
       sl messaging topic detail <account_id> <topic_name> [options]
       sl messaging topic create <account_id> <topic_name> [options]
       sl messaging topic delete <account_id> <topic_name> [<subscription_id>] [options]
       sl messaging topic push <account_id> <topic_name> (<message> | [-]) [options]

Manage topics and subscriptions

Topic/Subscription Create Options:
  --subscription        Create a subscription
  --type=TYPE           Type of endpoint, [Options: http, queue]
  --queue-name=NAME     Queue name. Required if --type is queue
  --http-method=METHOD  HTTP Method to use if --type is http
  --http-url=URL        HTTP/HTTPS URL to use. Required if --type is http
  --http-body=BODY      HTTP Body template to use if --type is http

Topic Delete Options:
  --force  Flag to force the deletion of the topic even when there are subscriptions
```

I'm not entirely happy with how creating subscriptions works. The idea is to have the create/delete commands be able to create topics as well as subscriptions. This works well for deleting subscriptions but not well for creating them. It would look like this: `sl messaging topic create <account_id> <topic_id> --subscription --type=queue --queue_name=some_queue`. I'm just not sure what this should look like. I wish the entire thing was a bit flatter.