add a toString to Block objects
make default feature detail popup use getFeatureLabel and getFeatureDescription
Revert "make wigglevaluedisplay flag explicitly say "no data" when
there is no data"

This reverts commit e8948d01a4daaacff8d787373d5d8d0b0b0bd7da.
rewrite NCList synchronization logic to use promises, now finishCallback is actually always called after all featCallbacks
tweak look of segments glyph borders