Refactor reporting infrastructure.

Refactor reporting infrastructure.

The old set of report classes and functions inside
wizard.command were ripped out, reimplemented, and
placed inside wizard.report.  The new API is:

    report.make(logdir, "name1", "name2" ...)
    report.make_fresh(logdir, "name1" ...)

Where make will append to previous files, and make_fresh
will clear out previous files.  Semantics for --redo
are made correct, and seen is superceded for mass-upgrade.

One very visible change is mass-upgrade will output
percentages that might actually sum to 100%!

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>