Relicense to GPL-3.0-only and add SPDX license headers (#627)

Relicense this module to GPL-3.0 and add SPDX license headers to source
files:

- Replace the old license file with LICENSE.md (GPL-3.0-only)
- Update license references in documentation (where applicable)
- Add SPDX headers to source files
- Mark source files as GPL-3.0-or-later

To ensure compatibility with third-party dependencies under licenses
incompatible with GPL-2.0-only (such as Apache-2.0), Icinga Web and its
module ecosystem are being relicensed to GPL-3.0-only.

Source files are labeled GPL-3.0-or-later to preserve the option to
relicense under later GPL versions.

Author: lippserd

LICENSE

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2018 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use gipfl\Cli\Screen;

LICENSE.md

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2018 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use Exception;

application/clicommands/CheckCommand.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2018 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use gipfl\SimpleDaemon\Daemon;

application/clicommands/Command.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2021 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use Exception;

application/clicommands/DaemonCommand.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2018 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use Icinga\Module\Vspheredb\CheckPluginHelper;

application/clicommands/DbCommand.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2021 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use Icinga\Module\Vspheredb\Db;

application/clicommands/HealthCommand.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2018 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 class PerfCommand extends Command

application/clicommands/MigrationCommand.php

@@ -1,5 +1,8 @@
 <?php
 
+// SPDX-FileCopyrightText: 2021 Icinga GmbH <https://icinga.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 namespace Icinga\Module\Vspheredb\Clicommands;
 
 use gipfl\Translation\StaticTranslator;