this patch fixes several issues:

– fix #103 by always re-rendering resonator details.
  A follow-up patch could also avoid re-rendering resos if they did not
  change. Given that there are only a few on these high zoom levels, perf
  improvement might be negligible though.
- fix #91. This avoids drawing portals/links/fields again if they are
  hidden. The patch looks for those hidden entities and either removes
  them before re-drawing (portals) or skips re-drawing altogether:
- Fields and Links are assumed to never change as long as their GUID is
  the same. This avoids deleting and re-creating links/fields all the
  time and might improve speed. Haven’t tested though.