Expand templates inside of notify

This patch expands templates inside of the notify block, to allow for implementing 'hooks' in roles.

Example:
roles/hooked/main.yml:
```
---
- debug: Frobbing "{{thing}}"
  notify: $onUpdate
```
main.yml:
```
---
hosts: all
roles:
  - role: hooked
    thing: "Something"
    onUpdate:
      - reload
  - role: hooked
    thing: "Something Else"
    onUpdate:
      - reload
      - cleanup
handlers:
  - name: reload
    action: debug Reloaded
  - name: cleanup
    action: debug Cleaned up!
```

This results in the reload handler being executed once for each task, and the cleanup handler executing once for the second application of the hooked role.