Enhance To-do's

Some enhancements for to-do's:

• If a to-do is created directly (i.e. created outside a feature/initiative/...), it would be useful to be able to subsequently associate that with a particular feature/initiative/... without having to create another todo
• Being able to associate a to-do with multiple different features would be useful
• Ability to report all open to-do's, including those not linked with a feature, so that ongoing work can be tracked hierarchically would be useful