use 'order' argument to change the tasks order: by text or by date

[fabienli]

only 'text' option for the moment, to sort by task's text.
If not specified, the default order (page's name and position in the page) is still applied.

[fabienli]

Hi, let me know what you think of having a way to change the tasks order in the tasklist.
This PR is a first functional minimum feature to demonstrate it.
I can take care to update the documentation if you integrate this, or if you think we should add more options.

[fabienli]

I've also added the 'date' option to the order, with this Pull Request you can then use the two following sorting methods samples:
{{dolist>?status=UNDONE&limit=50&order=text}}
{{dolist>?status=UNDONE&limit=50&order=date}}