update QRCodeDialog

- remove unused #include <QDebug> and lblBTC label
- update Bitcoin input field to a BitcoinAmountField to allow Bitcoin unit selection
- use BitcoinUnits::format for the resulting amount parameter in the generated URI (always use BTC as per BIP21)
- move MAX_URI_LENGTH and EXPORT_IMAGE_SIZE to guiconstants.h
- add OptionsModel in AddressBookPage and use it in on_showQRCode_clicked() to pass it to QRCodeDialog
- add OptionsModel in QRCodeDialog to enable display unit updates
- add updateDisplayUnit() slot to be able to imediately update currently set bitcoin unit
- make all labels in the UI-file plain text
- resize dialog to match for an updated layout (fields are now stacked and new field)
- remove unused parameters from private slots
- only enable save button, when QR Code was generated
- show message when entered amound is invalid
- add read-only QPlainTextEdit field to output generated URI

src/qt/addressbookpage.h

@@ -7,6 +7,7 @@ namespace Ui {
     class AddressBookPage;
 }
 class AddressTableModel;
+class OptionsModel;
 
 QT_BEGIN_NAMESPACE
 class QTableView;
@@ -37,6 +38,7 @@ public:
     ~AddressBookPage();
 
     void setModel(AddressTableModel *model);
+    void setOptionsModel(OptionsModel *optionsModel);
     const QString &getReturnValue() const { return returnValue; }
 
 public slots:
@@ -46,6 +48,7 @@ public slots:
 private:
     Ui::AddressBookPage *ui;
     AddressTableModel *model;
+    OptionsModel *optionsModel;
     Mode mode;
     Tabs tab;
     QString returnValue;