Big-Ugly Style Update (#278)

* Bulk replaced tabs with spaces
* Bulk removed trailing whitespace from lines
* Replaced c-style comments with c++-style comments in file banners
* Replace nested namespace definitions with single concise definitions (C++17), this keeps the indentation more manageable
* Cleanup ordering and spacing of include directives
* Bulk renaming of header file extensions from '.h' to '.hpp'.
* Update CODING-STYLE.md
* Update target_compile_features from cxx_std_11 to cxx_std_20.
* Refresh .clang-format file.  Still needs a lot of tweaking.

model/Category.hpp

@@ -0,0 +1,52 @@
+//  Category.hpp
+//
+//  Copyright (C) 2013-2016  Jaye Evins <evins@snaught.com>
+//
+//  This file is part of gLabels-qt.
+//
+//  gLabels-qt 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.
+//
+//  gLabels-qt 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 gLabels-qt.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+#ifndef model_Category_hpp
+#define model_Category_hpp
+
+
+#include <QString>
+
+
+namespace glabels::model
+{
+
+        class Category
+        {
+
+        public:
+                Category() = default;
+                Category( const QString& id, const QString& name );
+                ~Category() = default;
+
+                QString id() const;
+                QString name() const;
+
+
+        private:
+                QString mId;
+                QString mName;
+
+        };
+
+}
+
+
+#endif // model_Category_hpp