ExplorerCreateFile: have some proper defaults

[ewerybody]

from #60 (comment)

Ok. We should have some defaults anyway. I'd suggest to have sth like:

• .ahk
  • encoding: UTF-8 (with BOM)
  • content:

    #SingleInstance, Force
    SendMode, Input
    SetWorkingDir, %A_ScriptDir%

• .txt
  • encoding: UTF-8-RAW (without BOM)
  • no content
• .py
  • encoding: UTF-8-RAW (without BOM)

    def main():
        pass
    
    if __name__ == '__main__':
        main()

currently there is NONE!