Feature/add elb resource suppport

[BenCoffeed]

Adds ability to specify a Resource Logical name for implementations that create load balancers and target groups within the resource sections of the serverless.yml file. This is important because the CloudFormation update task will fail if the referenced target group is not already associated with an existing ELB. Ultimately, we should probably weigh whether we want to

1. continue support in this manner.
2. configure the plugin such that a target group + elb are created VIA the plugin and disable support for pre-existing target groups
   or
3. Find a way to both support existing target groups OR have the plugin create a new target group/elb pair and set dependencies accordingly.