Add download queue features from J2K fork

app/src/main/java/eu/kanade/tachiyomi/source/model/Page.kt

@@ -20,15 +20,23 @@ open class Page(
         set(value) {
             field = value
             statusSubject?.onNext(value)
+            statusCallback?.invoke(this)
         }
 
     @Transient
     @Volatile
     var progress: Int = 0
+        set(value) {
+            field = value
+            statusCallback?.invoke(this)
+        }
 
     @Transient
     private var statusSubject: Subject<Int, Int>? = null
 
+    @Transient
+    private var statusCallback: ((Page) -> Unit)? = null
+
     override fun update(bytesRead: Long, contentLength: Long, done: Boolean) {
         progress = if (contentLength > 0) {
             (100 * bytesRead / contentLength).toInt()
@@ -41,6 +49,10 @@ open class Page(
         this.statusSubject = subject
     }
 
+    fun setStatusCallback(f: ((Page) -> Unit)?) {
+        statusCallback = f
+    }
+
     companion object {
         const val QUEUE = 0
         const val LOAD_PAGE = 1