MW/PaletteWidget: Move palette/translation handling to PaletteWidget

Currently we are splitting the palette/translation handling between `MainWindow` class and `PaletteWidget`, so this patch changes that by moving the whole logic for handling color palettes that was contained in MainWindow to PaletteWidget and unifies it, so all of the handling happens here, instead of MainWindow.

I also found a lot of duplicated logic in MainWindow for translation palletes, uniq translation and normal palettes, I've tried to unify it as much as I could.

source/d1formats/d1trn.cpp

@@ -1,13 +1,13 @@
 #include "d1trn.h"
 
 D1Trn::D1Trn(D1Pal *pal)
-    : palette(QPointer<D1Pal>(pal))
+    : palette(pal)
 {
 }
 
 bool D1Trn::load(QString filePath)
 {
-    if (this->palette.isNull())
+    if (this->palette == nullptr)
         return false;
 
     QFile file = QFile(filePath);
@@ -73,6 +73,16 @@ QString D1Trn::getFilePath()
     return this->trnFilePath;
 }
 
+QString D1Trn::getDefaultPath() const
+{
+    return IDENTITY_PATH;
+}
+
+QString D1Trn::getDefaultName() const
+{
+    return IDENTITY_NAME;
+}
+
 quint8 D1Trn::getTranslation(quint8 index)
 {
     return this->translations[index];

source/d1formats/d1trn.h

@@ -6,7 +6,7 @@
 
 #define D1TRN_TRANSLATIONS 256
 
-class D1Trn : public QObject {
+class D1Trn final : public D1Pal {
     Q_OBJECT
 
 public:
@@ -17,15 +17,19 @@ class D1Trn : public QObject {
     D1Trn(D1Pal *pal);
     ~D1Trn() = default;
 
-    bool load(QString);
-    bool save(QString);
+    bool load(QString filepath) override;
+    bool save(QString filepath) override;
 
-    bool isModified() const;
+    [[nodiscard]] bool isModified() const override;
 
     void refreshResultingPalette();
     QColor getResultingColor(quint8);
 
-    QString getFilePath();
+    QString getFilePath() override;
+
+    [[nodiscard]] QString getDefaultPath() const override;
+    [[nodiscard]] QString getDefaultName() const override;
+
     quint8 getTranslation(quint8);
     void setTranslation(quint8, quint8);
     void setPalette(D1Pal *pal);
@@ -35,6 +39,6 @@ class D1Trn : public QObject {
     QString trnFilePath;
     bool modified;
     quint8 translations[D1TRN_TRANSLATIONS];
-    QPointer<D1Pal> palette;
+    D1Pal* palette = nullptr;
     D1Pal resultingPalette;
 };