Proposed New Journal Tiddler implementation

Addressing issue 336, https://github.com/Jermolene/TiddlyWiki5/issues/336 

Creates:
New widget message: tm-new-journal-tiddler
New handler : NavigatorWidget.prototype.handleNewJournalEvent = function(event)

Todo: 
work out date parsing for generated journal-tiddler title 
documentation 

Usage:
Widget message "tm-new-journal-tiddler" takes uses event.param to get name of a template tiddler
A proper journal tiddler will have a field "title_template" including date codes that will be converted upon creation of new tiddler draft.
if template tiddler in event.param does not exist NavigatorWidget does nothing.
if  field "title_template" does not exist in the template tiddler then handleNewJournalEvent's  behaviors defaults to that of handleNewTiddlerEvent .