Add support for resource types in policy generation

This code snippet is a simplified version of the examples in the [Boto3 docs](http://boto3.readthedocs.io/en/latest/guide/dynamodb.html#getting-an-item)

```
import boto3

db = boto3.resource("dynamodb")
tbl = db.Table('mytable')
r = tbl.get_item(Key={'mykey': myval})
```

The policy generator misses that this will need to add a `dynamodb:GetItem`.

In contrast, the policy generator does notice it when using this (more low-level) snippet:

```
dbc = boto3.client("dynamodb")
r = dbc.get_item(TableName="mytable", Key={"mykey": {"S": myval }})
```

Start by reproducing the two Boto3 examples in the issue and inspect the policy generator's handling of DynamoDB calls. Compare how client and resource API calls are identified. Done means the resource-based get_item example produces a policy containing dynamodb:GetItem, with the existing low-level behavior preserved.

Written by the indexing model from the issue text.