Added State Machine to target/provider images

You can generate a jpeg graph of the state machine defined in both the target_image and provider_image class (NOTE they both use the same state machine) using the following rake command:

```
rake state_machine:draw FILE=../../app/models/tim/target_image.rb CLASS=Tim::TargetImage
rake state_machine:draw FILE=../../app/models/tim/provider_image.rb CLASS=Tim::ProviderImage
```