Add support for Fn::Transform

*cfn-lint version: 0.7.4*

*Description of issue.*

cfn-lint does not properly evaluate Fn::Transform.

Example:

```yaml
Resources:

'Fn::Transform':
Name: 'AWS::Include'
Parameters:
Location: "s3://mybucket/mySnippet.yaml"

'Fn::Transform':
Name: 'AWS::Include'
Parameters:
Location: "s3://mybucket/mySecondSnippet.yaml"
```

Returns:
> Illegal cfn - missing Type: id: Fn::Transform

Additionally, multiple Fn::Transforms produce this error:
> Duplicate resource found "Fn::Transform" (line 299)

The template used which generated these errors passed `aws cloudformation validate-template` without error, so it is valid CFN syntax.

Reproduce the reported errors with the YAML example and compare the result with AWS CloudFormation validation. Trace how cfn-lint handles Fn::Transform under Resources, including repeated transforms, and consider the issue complete when valid transforms no longer trigger missing-Type or duplicate-resource errors.

Written by the indexing model from the issue text.