Make it easier to work with week notes

Until I have support for updating posts in my editor (as part of #285) I need some way to more easily edit my week notes - or at least, starting the process, as it's a little awkward to open up Micropublish and write the URL out manually, especially as I'm often doing this from mobile.

To make it easier, we can create links on the editor home page which kicks off the process for updating this/last week's notes, as they're most common, and to auto-fill the creation of this week's notes.