Cleaned up CustomTypesEditor and made it auto-save values

When adding, removing or changing values, the custom types are now
automatically saved. The explicit "Load" and "Save" buttons have been
removed, as well as the "Debug" button.

Also switched it from using a QTableWidget to a QTreeView and a model
derived from QStringListModel for the values.

Empty values are no longer automatically removed and new values get a
default text.

src/libtiled/customtype.cpp

@@ -32,18 +32,6 @@ namespace Tiled {
 
 int CustomType::nextId = 0;
 
-void CustomType::addValue(const QString &name)
-{
-    values << name;
-    validateValues();
-}
-
-void CustomType::validateValues()
-{
-    values.removeAll(QString());
-    values.removeDuplicates();
-}
-
 QVariant CustomType::wrap(QVariant value) const
 {
     return QVariant::fromValue(CustomValue { value, id });

src/libtiled/customtype.h

@@ -53,9 +53,6 @@ class TILEDSHARED_EXPORT CustomType
 
     static int nextId;
 
-    void addValue(const QString &name);
-    void validateValues();
-
     QVariant wrap(QVariant value) const;
     QVariant defaultValue() const;
 

src/libtiled/properties.h

@@ -1,6 +1,6 @@
 /*
  * properties.h
- * Copyright 2010, Thorbjørn Lindeijer <[email protected]>
+ * Copyright 2010-2021, Thorbjørn Lindeijer <[email protected]>
  *
  * This file is part of libtiled.
  *