Apply open document shortcuts to the tree that has focus (#945)

* Better handling of Enter/Return on GUI trees, resolves #913
* Update test
* Generalise open selected handle functions
* Improve test coverage
* Update docstring

tests/test_gui/test_gui_mainmenu.py

@@ -29,7 +29,7 @@ from PyQt5.QtWidgets import QAction, QFileDialog, QMessageBox
 from tools import writeFile
 
 from novelwriter.gui.doceditor import GuiDocEditor
-from novelwriter.enum import nwDocAction, nwDocInsert, nwWidget
+from novelwriter.enum import nwDocAction, nwDocInsert
 from novelwriter.constants import nwKeyWords, nwUnicode
 
 keyDelay = 2
@@ -471,11 +471,7 @@ def testGuiMenu_Insert(qtbot, monkeypatch, nwGUI, fncDir, fncProj):
     assert nwGUI.newProject({"projPath": fncProj})
 
     assert nwGUI.treeView._getTreeItem("0e17daca5f3e1") is not None
-
-    nwGUI.switchFocus(nwWidget.TREE)
-    nwGUI.treeView.clearSelection()
-    nwGUI.treeView._getTreeItem("0e17daca5f3e1").setSelected(True)
-    assert nwGUI.openSelectedItem()
+    assert nwGUI.openDocument("0e17daca5f3e1") is True
     nwGUI.docEditor.clear()
 
     # Test Faulty Inserts