Handle 'until' and 'recur' simiar to handling of 'gc' (#3753)

This centralizes updates to recurrence and 'until' in Command, instead
of doing so in each individual command implementation.

This is preparatory to opening the TaskChampion replica in read-only
mode.

src/commands/CmdEdit.cpp

@@ -64,6 +64,7 @@ CmdEdit::CmdEdit() {
   _read_only = false;
   _displays_id = false;
   _needs_gc = false;
+  _needs_recur_update = false;
   _uses_context = true;
   _accepts_filter = true;
   _accepts_modifications = false;