Bitcoin-Qt: translation fixes in sendcoins

- remove some unneeded translatable strings from sendcoinsentry.ui file and
  rename some elements for better readability
- optimize string prorcessing in SendCoinsDialog::on_sendButton_clicked()
- make all UI labels for secure payments plain text and move the settings
  to sendcoinsentry.ui file
- remove unneeded button and default button definiton from warning message
  boxes
- remove fixed font-size when sending coins to an address with label and
  use monospace font for addresses

src/qt/sendcoinsentry.h

@@ -33,7 +33,8 @@ public:
     void setValue(const SendCoinsRecipient &value);
     void setAddress(const QString &address);
 
-    /** Set up the tab chain manually, as Qt messes up the tab chain by default in some cases (issue https://bugreports.qt-project.org/browse/QTBUG-10907).
+    /** Set up the tab chain manually, as Qt messes up the tab chain by default in some cases
+     *  (issue https://bugreports.qt-project.org/browse/QTBUG-10907).
      */
     QWidget *setupTabChain(QWidget *prev);