Clarifies license to prevent any disputes

HEADER

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+Stargate - A portal plugin for Bukkit
+Copyright (C) 2011 Shaun (sturmeh)
+Copyright (C) 2011 Dinnerbone
+Copyright (C) 2011-2013 Steven "Drakia" Scott <Contact@TheDgtl.net>
+Copyright (C) 2015-2020 Michael Smith (PseudoKnight)
+Copyright (C) 2021-2022 Kristian Knarvik (EpicKnarvik97)
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.