Split callbacks in the CallbackManager

[jan-tennert]

What kind of change does this PR introduce?

Improvement

What is the current behavior?

• All callbacks (broadcast, presence, postgres) are stored in a single list

What is the new behavior?

• Split callbacks in three different lists / maps.
  • For broadcast callback a map is used, a callback list is stored under the respective event name
  • For presence callbacks a map is used, callbacks are mapped by their callback id for easy removal
  • Same with postgres callbacks