Log free heap memory

app/src/main/java/eu/faircode/email/Helper.java

@@ -614,4 +614,15 @@ public class Helper {
         bundle.writeToParcel(p, 0);
         return p.dataSize();
     }
+
+    static long getFreeMem() {
+        Runtime rt = Runtime.getRuntime();
+        long used = (rt.totalMemory() - rt.freeMemory());
+        long max = rt.maxMemory();
+        return (max - used);
+    }
+
+    static int getFreeMemMb() {
+        return (int) (getFreeMem() / 1024L / 1024L);
+    }
 }