Merge bitcoin-core/gui#251: Improve URI/file handling message

ef3e1d7272 qt: Improve URI/file handling message (Hennadii Stepanov)

Pull request description:

  This PR:
  - fixes missing spaces after full stops
  - makes the translation context much bigger

  The latter is the main motivation for this PR, as I became a translator 🐅

  Screenshots:
  - master (a9d1b40d53)

  ![DeepinScreenshot_select-area_20210317211750](https://user-images.githubusercontent.com/32963518/111527570-bd776880-8768-11eb-9035-96bb08067e74.png)

  - this PR:

  ![Screenshot from 2021-03-17 21-13-36](https://user-images.githubusercontent.com/32963518/111527727-e7308f80-8768-11eb-95c7-e8b802bfed5f.png)

ACKs for top commit:
  jarolrod:
    ACK ef3e1d7272

Tree-SHA512: 8fbd1e3731b75866356fae201b3129126001600ca0197e83c05825e8c5bbbcf0132d6a6b808d7a5cbfbdde75ed1865ecbb651c30017570abd7c5803eff2b9306

src/qt/paymentserver.cpp

@@ -235,9 +235,9 @@ void PaymentServer::handleURIOrFile(const QString& s)
                 if (!IsValidDestinationString(recipient.address.toStdString())) {
                     if (uri.hasQueryItem("r")) {  // payment request
                         Q_EMIT message(tr("URI handling"),
-                            tr("Cannot process payment request because BIP70 is not supported.")+
-                            tr("Due to widespread security flaws in BIP70 it's strongly recommended that any merchant instructions to switch wallets be ignored.")+
-                            tr("If you are receiving this error you should request the merchant provide a BIP21 compatible URI."),
+                            tr("Cannot process payment request because BIP70 is not supported.\n"
+                               "Due to widespread security flaws in BIP70 it's strongly recommended that any merchant instructions to switch wallets be ignored.\n"
+                               "If you are receiving this error you should request the merchant provide a BIP21 compatible URI."),
                             CClientUIInterface::ICON_WARNING);
                     }
                     Q_EMIT message(tr("URI handling"), tr("Invalid payment address %1").arg(recipient.address),
@@ -258,9 +258,9 @@ void PaymentServer::handleURIOrFile(const QString& s)
     if (QFile::exists(s)) // payment request file
     {
         Q_EMIT message(tr("Payment request file handling"),
-            tr("Cannot process payment request because BIP70 is not supported.")+
-            tr("Due to widespread security flaws in BIP70 it's strongly recommended that any merchant instructions to switch wallets be ignored.")+
-            tr("If you are receiving this error you should request the merchant provide a BIP21 compatible URI."),
+            tr("Cannot process payment request because BIP70 is not supported.\n"
+               "Due to widespread security flaws in BIP70 it's strongly recommended that any merchant instructions to switch wallets be ignored.\n"
+               "If you are receiving this error you should request the merchant provide a BIP21 compatible URI."),
             CClientUIInterface::ICON_WARNING);
     }
 }