Allow out-of-process edits to keymappings.json

Reloads keymappings.json on each client join. This allows for manual edits,
so host can add keys without having to restart server for them to go live.

src/network/network.cpp

@@ -1431,7 +1431,6 @@ void Network::SaveKeyMappings()
 
 void Network::LoadKeyMappings()
 {
-	group_list.clear();
 
 	utf8 path[MAX_PATH];
 
@@ -1441,6 +1440,7 @@ void Network::LoadKeyMappings()
 	if (!platform_file_exists(path)) {
 		return;
 	}
+	key_group_map.clear();
 
 	json_t * jsonKeyMappings = Json::ReadFromFile(path);
 
@@ -1900,6 +1900,8 @@ NetworkPlayer* Network::AddPlayer(const std::string &keyhash)
 		newid = 0;
 	}
 	if (newid != -1) {
+		// Load keys host may have added manually
+		LoadKeyMappings();
 		std::unique_ptr<NetworkPlayer> player(new NetworkPlayer); // change to make_unique in c++14
 		player->id = newid;
 		player->keyhash = keyhash;