Presalytics

* Eliminate overwrite error in cli

* Fix cli initial pull in empty workspace
* Fix cli default to CACHE_TOKENS = True

* Add events handling to widgets with nested iframes

* Fix page css clases

* Fix json encoder in `presalytics.lib.widgets.datatable.DataTableWidget`
* update Story Api Endpoints

* Point `ooxml.js` to static folder on main site in `presalytics.lib.plugins.external.ApprovedExternalScripts`
* Add `presalytics.lib.widgets.url.UrlWidget`
* Add `presalytics.lib.widgets.chart.ChartWidget`
* Add `presalytics.lib.widgets.datatable.DataTableWidget`
* Fix immutability bug in `presalytics.lib.plugins.reveal.RevealConfigPlugin.default_config`