Changed occurences of 'widget' to 'area' in code.

src/__init__.py

src/area.py

src/areas.py

src/event.py

src/event_driver.py

src/event_server.py

src/tracker.py

src/trackers/tap.py

src/trackers/transform.py

tests/basic.py

tests/cairotest.py

tests/draw.py

tests/tap.py

tests/transform.py