and more fixes

* fix content length reading
* use float overflow. Expensive, double is used instead
* fix invalid cast after click the mission body
* use a list for maximum attemps (downloads)
* minor clean up (DownloadManager.java)
* dont pass SharedPreferences instace to DownloadManager
* use a switch instead of checkbox for cross_network_downloads
* notify media scanner after deleting a finished download

app/src/main/java/us/shandian/giga/get/DownloadRunnable.java

@@ -89,7 +89,7 @@ public class DownloadRunnable implements Runnable {
                 end = mMission.length - 1;
             }
 
-            int total = 0;
+            long total = 0;
 
             try {
                 HttpURLConnection conn = mMission.openConnection(mId, start, end);