A good Celtics fan friend of mine likes to talk about the five seasons: winter, spring, summer, fall, and trade season. While there’s not much else to like about February in New England, the prospect of change at the NBA’s Feb. 20 deadline for teams to make deals offers a glimmer of sunnier times ahead. This year in particular is interesting for the Celtics; in recent seasons, the deadline has been a place to make minor additions on the way to a championship run. With the team rebuilding, everyone is in play. Last week, we discussed which Celtics may be on the block. Now comes the fun part: which players, some of them big stars, would be good fits in Boston?