Fixed the traceback which comes while creating/modifying of HTML wiki

While creating HTML wiki a traceback comes specifying basic_data_editor is not defined but it is defined for all other types of wiki.So added an if statement in the themes/basic/templates/modify.html that is the basic_data_editor is defined then use it else use data_editor. basic_data_editor was not working because it is defined only for the basic wiki but in html wiki some special widgets are required which are taken from the data_editor.