Add Delete functionality. Still buggy.

app/project/projectviewmodel.h

@@ -25,6 +25,7 @@
 
 #include "project.h"
 #include "undo/undocommand.h"
+#include "node/block/block.h"
 
 OLIVE_NAMESPACE_ENTER
 
@@ -215,6 +216,29 @@ public:
     QMap<Node*, StreamPtr> nodes_;
   };
 
+  class DeleteFootageCommand : public UndoCommand {
+  public:
+    DeleteFootageCommand(ProjectViewModel* model, ItemPtr item, QList<Block*> blocks, QUndoCommand* parent = nullptr);
+
+    virtual Project* GetRelevantProject() const override;
+
+  protected:
+    virtual void redo_internal() override;
+
+    virtual void undo_internal() override;
+
+  private:
+    ProjectViewModel* model_;
+
+    ItemPtr item_;
+
+    QList<Block*> blocks_;
+
+    QUndoCommand* deleteCommand_;
+
+    QUndoCommand* removalCommand_;
+  };
+
 private:
   /**
    * @brief Retrieve the index of `item` in its parent