Added new logger.

Added a new logger that persists logs for a longer duration to the
user's cache directory. Logs are encrypted. The new logs are sent
in addition to the user's logcat output.

src/org/thoughtcrime/securesms/crypto/KeyStoreHelper.java

@@ -152,7 +152,7 @@ public class KeyStoreHelper {
       }
     }
 
-    static SealedData fromString(@NonNull String value) {
+    public static SealedData fromString(@NonNull String value) {
       try {
         return JsonUtils.fromJson(value, SealedData.class);
       } catch (IOException e) {