ENYO-2106: rename ide.json into ide.plugin.json

The is the simplest way I found to make sure that Ares does not consider
its own `ide.json` as a plugin configuration file when both Ares & its
plugins are installed as similar modules using NPM.

This change demands (of course) the dual change in plugin's source.

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>