Merge 0.5.7 (#88)

* Add null checks

* update label

* capitalization and update translations

* v0.5.7

* Don't show error on cancel

src/mainwindow.h

@@ -90,7 +90,6 @@ private:
 
     void donate();
     void addressBook();
-    void payZcashURIError(QString errorDetail = "");
     void payZcashURI();
     void postToZBoard();
     void importPrivKey();