-Fixed NPE issues when button views are clicked on local playlist and statistics playlist fragments are out of focus.

-Added disk cache size limit for image loader.
-Fixed button names for playlist rename dialog.

app/src/main/res/values/strings.xml

@@ -233,6 +233,7 @@
     <string name="delete_all">Delete All</string>
     <string name="checksum">Checksum</string>
     <string name="dismiss">Dismiss</string>
+    <string name="rename">Rename</string>
 
     <!-- Fragment -->
     <string name="add">New mission</string>