Editor: Cleanup some includes dependencies

Removes some unnecessary includes from `editor_node.h`, and instead add
those where they're used.

Removes unnecessary `editor_node.h` includes in various editor classes.

Renames `dynamicfont` to `dynamic_font` in a couple files.

Misc cleanup while jumping through that rabbit hole.

editor/editor_data.h

@@ -33,11 +33,11 @@
 
 #include "core/object/undo_redo.h"
 #include "core/templates/list.h"
-#include "core/templates/pair.h"
-#include "editor/editor_plugin.h"
-#include "editor/plugins/script_editor_plugin.h"
 #include "scene/resources/texture.h"
 
+class ConfigFile;
+class EditorPlugin;
+
 class EditorHistory {
 	enum {
 		HISTORY_MAX = 64
@@ -59,8 +59,6 @@ class EditorHistory {
 	Vector<History> history;
 	int current;
 
-	//Vector<EditorPlugin*> editor_plugins;
-
 	struct PropertyData {
 		String name;
 		Variant value;