Add 'About Porymap' window that contains useful information about the program

src/mainwindow.cpp

@@ -1,5 +1,6 @@
 #include "mainwindow.h"
 #include "ui_mainwindow.h"
+#include "aboutporymap.h"
 #include "project.h"
 #include "log.h"
 #include "editor.h"
@@ -1859,6 +1860,13 @@ void MainWindow::on_toolButton_CollapseAll_clicked()
     }
 }
 
+void MainWindow::on_actionAbout_Porymap_triggered()
+{
+    AboutPorymap *window = new AboutPorymap(this);
+    window->setAttribute(Qt::WA_DeleteOnClose);
+    window->show();
+}
+
 void MainWindow::closeEvent(QCloseEvent *event) {
     porymapConfig.setGeometry(
         this->saveGeometry(),

src/ui/aboutporymap.cpp

@@ -0,0 +1,14 @@
+#include "aboutporymap.h"
+#include "ui_aboutporymap.h"
+
+AboutPorymap::AboutPorymap(QWidget *parent) :
+    QMainWindow(parent),
+    ui(new Ui::AboutPorymap)
+{
+    ui->setupUi(this);
+}
+
+AboutPorymap::~AboutPorymap()
+{
+    delete ui;
+}