overlay: create a dedicated thread for polling hotkeys (#864)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Create a new thread that polls for the following hotkeys:

* super exit (both alt+f4 and bound key)
* coin insert
* screenshot

The goal is to make the capture of these more reliable, because before
this PR it wasn't.

## Testing

src/spice2x/misc/eamuse.h

@@ -58,9 +58,7 @@ bool eamuse_coin_consume(int amount);
 int eamuse_coin_consume_stock();
 
 int eamuse_coin_add();
-
-void eamuse_coin_start_thread();
-void eamuse_coin_stop_thread();
+void eamuse_coin_insert();
 
 void eamuse_pin_macro_start_thread();
 void eamuse_pin_macro_stop_thread();