Internal: Reduce inconsistency in $forceShow API.

$forceShow, recall, is the "override conflicts" button on papers with
which the chair is conflicted. In some situations the "override
conflicts" setting should be ignored. The APIs for obeying $forceShow
were inconsistent, which led to some minor bugs. Make them more
consistent: $forceShow === null means check $_REQUEST; otherwise treat
$forceShow as a truth value for whether to force.
Nitlet: New session lists contain q= parameters whenever they should.
Nitlet: Correctly handle PaperConflict rows with conflictType<=0.
Internal: For consistency, author queries also define a null reviewType.
Internal: Complete refactoring of list columns into smarter objects.

Each object knows whether it's allowed to render for a given user.
Which would make it safe for a user to request a named column (it
wasn't safe before).