Discord RPC cleanup

- Loading Discord RPC is now handled by `load/rpc.lua`
- Removed `presence` global, call `DiscordRPC:update()` directly with what needs updating
- Game doesn't crash anymore if the Discord RPC fails to load
- Added RPC variables in the gamemode superclass to let each gamemode handle its special case

load/rpc.lua

@@ -0,0 +1,56 @@
+print("Loading discord RPC...")
+DiscordRPC = {
+    loaded = false
+}
+local success, RPC = pcall(require, "libs.discordRPC")
+if success then
+    DiscordRPC.loaded = true
+    DiscordRPC.appId = "599778517789573120"
+
+    function RPC.ready(userId, username, discriminator, avatar)
+        print(string.format("Discord: ready (%s, %s, %s, %s)", userId, username, discriminator, avatar))
+    end
+
+    function RPC.disconnected(errorCode, message)
+        print(string.format("Discord: disconnected (%d: %s)", errorCode, message))
+    end
+
+    function RPC.errored(errorCode, message)
+        print(string.format("Discord: error (%d: %s)", errorCode, message))
+    end
+
+    function RPC.joinGame(joinSecret)
+        print(string.format("Discord: join (%s)", joinSecret))
+    end
+
+    function RPC.spectateGame(spectateSecret)
+        print(string.format("Discord: spectate (%s)", spectateSecret))
+    end
+
+    function RPC.joinRequest(userId, username, discriminator, avatar)
+        print(string.format("Discord: join request (%s, %s, %s, %s)", userId, username, discriminator, avatar))
+        RPC.respond(userId, "yes")
+    end
+
+    RPC.initialize(DiscordRPC.appId, true)
+    local now = os.time(os.date("*t"))
+	RPC.updatePresence({
+            startTimestamp = now,
+            details = "Loading game...",
+            state = "",
+            largeImageKey = "icon2",
+            largeImageText = "Original game by Joe Zeng",
+            smallImageKey = "",
+            smallImageText = ""
+    })
+    
+    DiscordRPC.RPC = RPC
+    print("DiscordRPC successfully loaded.")
+else
+    print("DiscordRPC failed to load!")
+    print(RPC)
+end
+
+function DiscordRPC:update(newstuff)
+    if self.loaded then self.RPC.updatePresence(newstuff) end
+end