fix some cosmetic glitches in the codebase

- rename URL into URI in paymentserver where correct
- add some missing Qt-coding-stuff in paymentserver
- change QSpinBox to QLineEdit as base for BitcoinAmountField in .ui files
  (as this is the result when converting the BAF back into base)
- remove some c_str() and replace with QString::fromStdString()
- remove several new-lines
- remove unneeded spaces
- indentation fixes

src/qt/paymentrequestplus.cpp

@@ -80,7 +80,7 @@ bool PaymentRequestPlus::getMerchant(X509_STORE* certStore, QString& merchant) c
         return false;
     }
     else {
-        qDebug() << "PaymentRequestPlus::getMerchant : Payment request: unknown pki_type " << paymentRequest.pki_type().c_str();
+        qDebug() << "PaymentRequestPlus::getMerchant : Payment request: unknown pki_type " << QString::fromStdString(paymentRequest.pki_type());
         return false;
     }
 
@@ -152,7 +152,7 @@ bool PaymentRequestPlus::getMerchant(X509_STORE* certStore, QString& merchant) c
         // Valid cert; check signature:
         payments::PaymentRequest rcopy(paymentRequest); // Copy
         rcopy.set_signature(std::string(""));
-        std::string data_to_verify;                 // Everything but the signature
+        std::string data_to_verify;                     // Everything but the signature
         rcopy.SerializeToString(&data_to_verify);
 
         EVP_MD_CTX ctx;