Rename smurf named methods

[dturner]

Here's what I've done and why:

• Removed Task from TaskRepository methods to avoid smurf naming e.g createTask becomes just create.
• Changed get to observe for methods which return a Flow. This is less verbose and more accurate than getTaskStream.
• Methods which return a List<Task> have All after the verb e.g. observeAll and `clearAllCompleted.