Add support for a forums application and a mongo database.
Give Edxapp instance s3 and ses permissions.
Minor Worker application related fixes.

Make sure the workers reference the correct wait handle and are in the RDS security group.
Updates to change the device names and update network acls.
Default to 3 mongo instances so that clusters do not need an arbiter.
Fix worker wait condition to wait for worker servers.
Remove scaling policies and scaling alarms.
Use a for look for repetative code.
Update instance tags to match new scheme.
Add the worker to the elasticache security group.
VPC DNS and Elasticache support

I hope this helps cleaning up a bit.
Added ability for mongo role to do simple replica set clusters
By default this should keep the role the same.  The only catch with this implementation
is that the ansible mongodb_user module doesn't handle slaves particularly well. So if you
have a cluster than any task that creates a user will succeed on the master and fail on all
slaves.
Corrections and fixes to match what the manual command used to do.
Fix cache references and correct subnet names.
Remove EdxServerUser since we have IAM roles setup for all application instance types.
Add a third subnet for mongo in a third AZ since there will be at minimum 3 instances.
Begin using us-east-1d AZ since we can't create subnets in us-east-1a
Merge pull request #346 from edx/feanil/forums_cfn

Feanil/forums cfn
Merge pull request #299 from edx/carsongee/mongo_cluster_support

Added ability for mongo role to do simple replica set clusters
updating from master, merge conflicts