Implement global and per instance shader uniforms.

Adds two keywords to shader language for uniforms:
-'global'
-'instance'

This allows them to reference values outside the material.

editor/project_settings_editor.h

@@ -36,6 +36,7 @@
 #include "editor/editor_data.h"
 #include "editor/editor_plugin_settings.h"
 #include "editor/editor_sectioned_inspector.h"
+#include "editor/shader_globals_editor.h"
 #include "scene/gui/dialogs.h"
 #include "scene/gui/tab_container.h"
 
@@ -85,6 +86,7 @@ class ProjectSettingsEditor : public AcceptDialog {
 	OptionButton *device_index;
 	Label *device_index_label;
 	MenuButton *popup_copy_to_feature;
+	ShaderGlobalsEditor *shaders_global_variables_editor;
 
 	LineEdit *action_name;
 	Button *action_add;