Now that debconf-apt-progress is used and tasksel can run inside debconf,
it would be nice to convert it so tasksel starts debconf in the beginning,
and runs everything under debconf, except perhaps any manual package
selection that the user might decide to do. This would reduce startup
delays and also the delay between the two debconf runs it does now.

Also, to better handle the case of one task being removed while another is
installed, use debconf-apt-progress with waypoints.

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Move more data from tasks/* to task packages.