in newEntry, rebuild all tabs (a slow process - see #670) when unhiding a tab, whether by GUI from the sidebar, or by a new entry from typed callsign or from fleetsync; otherwise, call addTab individually
in rebuildGroupedTabDict, don't add a spacer after a group if all of that group's tab(s) are hidden
in deleteTeamTab, break the loop upon finding back-to-back spacers and deleting one of them - this fix might be rendered moot by the fixes above
fix #766