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/csvmodelwriter.cpp

@@ -85,4 +85,3 @@ bool CSVModelWriter::write()
 
     return file.error() == QFile::NoError;
 }
-