Build - improve Windows msi build script

Author: samaaron

install/windows/wix/gen_msi.bat

@@ -1,5 +1,10 @@
 cd %~dp0
 cd ..
+
+@echo "Remove old files"
+del /q /s /f *.wixobj
+del /q /s /f *.wixpdb
+del /q /s /f ReleaseFiles*
 @echo "Generating msi"
 candle wix\sonic-pi.wxs etc.wxs gui.wxs server.wxs config.wxs -ext WixUtilExtension -arch x64
 light sonic-pi.wixobj etc.wixobj gui.wixobj server.wixobj config.wixobj -ext WixUtilExtension -ext WixUIExtension -o wix\Sonic-Pi.msi -b etc -b app\gui -b app\server -b app\config