Rename IFile->IDocument and FileManager->DocumentManager

And adapt the other API respectively.

Change-Id: I1e04e555409be09242db6890f9e013396f83aeed
Reviewed-by: Bill King <bill.king@nokia.com>
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/glsleditor/glsleditor.cpp

@@ -420,7 +420,7 @@ TextEditor::IAssistInterface *GLSLTextEditorWidget::createAssistInterface(
     if (kind == TextEditor::Completion)
         return new GLSLCompletionAssistInterface(document(),
                                                  position(),
-                                                 editor()->file(),
+                                                 editor()->document(),
                                                  reason,
                                                  mimeType(),
                                                  glslDocument());