Improving the single-instance IPC

### Problem

The  MPC-HC playlist will only contain the items opened in the new instances when

* enable "Options → Player → Use the same player for each media file"
* open a folder in a new instance (command `mpc-hc.exe folder`) that takes longer than ,5 s to recurse

### Solution

Changing the single-instance IPC so that it waits for the new process to perform a time consuming task such as recursing through a large folder tree or multiple folders rather than resetting the playlist after a fixed amount of time

OnCopyData was previously limited to 500 ms but now has no limit

The ID_FILE_CLOSEMEDIA is removed because it causes a long delay between WM_COPYDATA messages, causing the playlist to reset. If it has to be there the allowed delay between WM_COPYDATA messages has to be increased to at least 2000 ms