SWF Editor - Add Icon to show there are subflows defined in States

There is no visual indication that there are subflows defined in the state. Currently the user has to go to the state definition in the text editor or hover action icon on the upper-right corner of the state to check for defined actions. 

The goal is to make easy to identify if there are subflows definitions in states by showing an icon representing subflows at the top-left of the state.

All states that implement "Actions" can implement a subflow:

• Callback State
• ForEach State
• Operation State
• Parallel State

Expected behavior:

• The icon shall be shown only if there are subflows defined in the state.
• No tooltip shall be displayed (since this information is already presented in the action icon tooltip).