Fix a few memory leaks; add /gc console command
3 memory leaks were fixed
  - ipThrottle (due to the periodic cleaner clearing the wrong object...)
  - ipCount (shouldn't have leaked very much, but removing obsolete data is good practice)
  - lastguestlogin (again, shouldn't leak much, but should be cleared periodically anyways)
A new console command (i.e. from the terminal running node) was added: /gc
  - If the process is invoked as node --expose-gc index.js, /gc allows you to manually invoke the garbage collector