Added Features: hide other users tracings, show nodes from adjacent sections

I added 2 new features:

1) hide other users tracings
  - added per-user setting to either hide or allow viewing of other users tracings
  - added db migration script

2) show nodes from +/- N adjacent sections
  - modified db query
  - modified tracing tools ui
  - modified some js ui calls to allow drawing of nodes with larger zdiffs