Add slf4j to mixins and expose logger in Hooks for them

runelite-mixins/pom.xml

@@ -37,6 +37,12 @@
 	<name>RuneLite Mixins</name>
 
 	<dependencies>
+		<dependency>
+			<groupId>org.slf4j</groupId>
+			<artifactId>slf4j-api</artifactId>
+			<version>1.7.21</version>
+			<scope>provided</scope>
+		</dependency>
 		<dependency>
 			<groupId>net.runelite.rs</groupId>
 			<artifactId>api</artifactId>

runelite-mixins/src/main/java/net/runelite/client/callback/Hooks.java

@@ -25,6 +25,7 @@
 package net.runelite.client.callback;
 
 import com.google.common.eventbus.EventBus;
+import org.slf4j.Logger;
 
 /**
  * Dummy class to make the mixins to compile.
@@ -33,5 +34,7 @@ import com.google.common.eventbus.EventBus;
  */
 public class Hooks
 {
+	public static Logger log;
+
 	public static EventBus eventBus;
 }