CBuilderManager::MakeTask chain lags

[rlcevg]

On large maps CBuilderManager::MakeTask seems to be the cause of lag spikes.
c792282 limits MakeTask calls, but doesn't look like absolute fix.

[rlcevg]

Current issue is calling circuit's pathfinder several times in single frame.

1. Reducing granularity of path-map improves performance greatly (4x). Previously only maps greater than 20x20 used path-map with low resolution. Changing barrier to 16x16.
2. Threading would also help a lot, but that's another story for another major AI version.
3. Another thing to consider - is additional heuristic for single start and multiple end points that should reduce number of pathfinder calls.

[rlcevg]

Reduced lag by threaded pathfinder