Keep the toolbar handle pinned to the side after drag event.

Current behaviour: after handle is moved when the window width is resized the handled keeps its absolute position rather than sticking to the right side of the window. Handle position returns to normal on page reload.
Don't suggest adding the app config to INSTALLED_APPS.

This is more in line with Django's contrib apps.

Fix #621.
Make note of the incompatability with the GZipMiddleware.