Updated Qt required version

As per the Wiki on building for OS X 
https://github.com/mcallegari/qlcplus/wiki/OSX-Build-HOWTO
Fixed Website Link in Aboutbox not working on Windows and URL adjusted.
Merge pull request #200 from pixeldoc2000/master

Fixed Website Link in Aboutbox not working on Windows and URL adjusted.
Merge pull request #199 from MichaelJames6/patch-1

Updated Qt required version for OSX
Merge branch 'master' of git://github.com/mcallegari/qlcplus