Fix float/int conversion error in TermFrequencyWeightPolicy
ConjunctionNode should not advance over children with zero weight
Slowlog should report times in ms
QueryTreeViewer now shows the selected term at each junction
Add Advancer API, for advancing a querytree through phases

By default, we don't advance a conjunction over a node with a weight of 0.
Decouple TreeAdvancer and TreeWeightor from node construction

These are now passed in at collection/advance time, allowing you to collect
terms from the same tree with different weights, or use different advancing
strategies for different phases.