GUI: merge sign/verify message into a single window with tabbed UI

- add UI-feedback via QValidatedLineEdit
- copy button for generated signature was moved to the signature output field
- add an addressbook button to verify message tab
- input fields are now evenly ordered for sign and verify tabs
- update FIRST_CLASS_MESSAGING support to ensure a good UX
- add a button and context menu entry in addressbook for verify message (to be consistent with sign message)
- focus is now only set/changed, when clearing input fields or adding an address via addressbook
- re-work / update some strings
- ensure model gets initialized in the SignVerifyMessageDialog constructor
- add checks for a valid model to both addressbook buttons
- remove unneeded includes for Qt GUI elements that are listed in ui_signverifymessagedialog.h anyway

src/qt/signverifymessagedialog.h

@@ -0,0 +1,49 @@
+#ifndef SIGNVERIFYMESSAGEDIALOG_H
+#define SIGNVERIFYMESSAGEDIALOG_H
+
+#include <QDialog>
+
+namespace Ui {
+    class SignVerifyMessageDialog;
+}
+class WalletModel;
+
+QT_BEGIN_NAMESPACE
+QT_END_NAMESPACE
+
+class SignVerifyMessageDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit SignVerifyMessageDialog(QWidget *parent = 0);
+    ~SignVerifyMessageDialog();
+
+    void setModel(WalletModel *model);
+    void setAddress_SM(QString address);
+    void setAddress_VM(QString address);
+
+    void showTab_SM(bool fShow);
+    void showTab_VM(bool fShow);
+
+protected:
+    bool eventFilter(QObject *object, QEvent *event);
+
+private:
+    Ui::SignVerifyMessageDialog *ui;
+    WalletModel *model;
+
+private slots:
+    /* sign message */
+    void on_addressBookButton_SM_clicked();
+    void on_pasteButton_SM_clicked();
+    void on_signMessageButton_SM_clicked();
+    void on_copySignatureButton_SM_clicked();
+    void on_clearButton_SM_clicked();
+    /* verify message */
+    void on_addressBookButton_VM_clicked();
+    void on_verifyMessageButton_VM_clicked();
+    void on_clearButton_VM_clicked();
+};
+
+#endif // SIGNVERIFYMESSAGEDIALOG_H