UI: Add file prefix/suffix options for replay buffer

Adds the ability to use a specific prefix and/or suffix on replay buffer
filenames to distinguish them from normal recordings.  Defaults to
having the prefix "Replay".

UI/window-basic-main.cpp

@@ -850,6 +850,8 @@ bool OBSBasic::InitBasicConfigDefaults()
 	config_set_default_bool(basicConfig, "SimpleOutput", "RecRB", false);
 	config_set_default_int(basicConfig, "SimpleOutput", "RecRBTime", 20);
 	config_set_default_int(basicConfig, "SimpleOutput", "RecRBSize", 512);
+	config_set_default_string(basicConfig, "SimpleOutput", "RecRBPrefix",
+			"Replay");
 
 	config_set_default_bool  (basicConfig, "AdvOut", "ApplyServiceSettings",
 			true);