dev#160166 : CkEditor placeholders plugin

This plugin adds 2 buttons (records and articles)
that print a corresponding placeholder.

dev#160166 : different to set plugin buttons on newsletter editor only

dev#160166 : replace ckeditor placeholders with bokeh entities

dev#160166 : mailrenderer widget

dev#160166 : Widget always send results Should be empty when no data selected

dev#160166 : Placeholders in renderwithwigdetContext tests