Add support for QScintilla

[Temujin2887]

Could you add an optional build script for QScintilla? I was able to get it to work for 2017/2018 using the following windows batch (Along with adding QSCINTILLADIR to setup.bat)

@echo off
set XXX=%~dp0
if ["%MAYAPYQTBUILD%"]==[""] call "%XXX%setup.bat"

set QMAKESPEC=%QTDIR%\mkspecs\%_QMAKESPEC_%

rem Build QScintilla
pushd %QSCINTILLADIR%\Qt4Qt5
qmake
nmake release
nmake release-install
popd

rem Build QScintilla designer plugin wrapper
pushd %QSCINTILLADIR%\designer-Qt4Qt5
qmake
nmake release
nmake release-install
popd


rem Build QScintilla python wrapper
pushd %QSCINTILLADIR%\Python
"%MAYA_LOCATION%\bin\mayapy" configure.py --pyqt=PyQt5 --sip %QTDIR%\Python\sip.exe
nmake
nmake install
popd

I added these lines to setup.bat:

set QSCINTILLAVERSION=2.10.1
set QSCINTILLADIR=%BUILDDRIVE%\QScintilla_gpl-%QSCINTILLAVERSION%

[iamsleepy]

I think we'll make the scripts only for building PyQt5 and sip right now.