Change license to GPLv3

[Joonalai]

Use following copyright template:

#set( $Foobar = "NLSgpkgloadert" )
Gispo Ltd., hereby disclaims all copyright interest in the program $Foobar
#if( ${today.year}  == 2018)
Copyright (C) ${today.year} Gispo Ltd (https://www.gispo.fi/).
#else
Copyright (C) 2018-${today.year} Gispo Ltd (https://www.gispo.fi/).
#end


This file is part of $Foobar.

$Foobar is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

$Foobar is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with $Foobar.  If not, see <https://www.gnu.org/licenses/>.