Added annotation overview windows:

- show this dockable window by default at the bottom of the main
  window;
- added it as listener for changes in the annotation data;
- improved the initial layout of the dockable windows.
Demo device incorrectly retained some state:

- the i2c, 1-wire and Manchester generators temporarily keep state
  in their implementation, but never cleared them. This caused them
  to always append data if used more than once.
Removed unused methods.
Prettified the annotations split out by tools a bit.