Refactor GameyfinPlugin and ConfigurableGameyfinPlugin to fix SLF4J issue

plugin-api/src/main/kotlin/de/grimsi/gameyfin/pluginapi/core/ConfigurableGameyfinPlugin.kt

@@ -0,0 +1,17 @@
+package de.grimsi.gameyfin.pluginapi.core
+
+import org.pf4j.PluginWrapper
+
+abstract class ConfigurableGameyfinPlugin(wrapper: PluginWrapper) : GameyfinPlugin(wrapper), Configurable {
+
+    companion object {
+        lateinit var plugin: ConfigurableGameyfinPlugin
+            private set
+    }
+
+    init {
+        plugin = this
+    }
+
+    override var config: Map<String, String?> = emptyMap()
+}

plugin-api/src/main/kotlin/de/grimsi/gameyfin/pluginapi/core/GameyfinPlugin.kt

@@ -8,6 +8,13 @@ abstract class GameyfinPlugin(wrapper: PluginWrapper) : Plugin(wrapper) {
     companion object {
         const val LOGO_FILE_NAME: String = "logo"
         val SUPPORTED_LOGO_FORMATS: List<String> = listOf("png", "jpg", "jpeg", "gif", "svg", "webp")
+
+        lateinit var plugin: GameyfinPlugin
+            private set
+    }
+
+    init {
+        plugin = this
     }
 
     fun hasLogo(): Boolean {