Add meson build system

data/de.johrpan.musicus.desktop.in

@@ -0,0 +1,7 @@
+[Desktop Entry]
+Name=Musicus
+Exec=musicus
+Terminal=false
+Type=Application
+Categories=GTK;
+StartupNotify=true

data/de.johrpan.musicus.gschema.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<schemalist gettext-domain="musicus">
+	<schema id="de.johrpan.musicus" path="/de/johrpan/musicus/">
+		<key name="music-library-path" type="s">
+			<default>""</default>
+			<summary>Path to the music library folder</summary>
+		</key>
+	</schema>
+</schemalist>

data/meson.build

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+desktop_file = i18n.merge_file(
+  input: 'de.johrpan.musicus.desktop.in',
+  output: 'de.johrpan.musicus.desktop',
+  type: 'desktop',
+  po_dir: '../po',
+  install: true,
+  install_dir: join_paths(get_option('datadir'), 'applications')
+)
+
+desktop_utils = find_program('desktop-file-validate', required: false)
+if desktop_utils.found()
+  test('Validate desktop file', desktop_utils,
+    args: [desktop_file]
+  )
+endif
+
+install_data('de.johrpan.musicus.gschema.xml',
+  install_dir: join_paths(get_option('datadir'), 'glib-2.0/schemas')
+)
+
+compile_schemas = find_program('glib-compile-schemas', required: false)
+if compile_schemas.found()
+  test('Validate schema file', compile_schemas,
+    args: ['--strict', '--dry-run', meson.current_source_dir()]
+  )
+endif