Plugins shared config

[GuilleAngulo]

Description

When a config object is passed to a plugin, the following plugins will share same settings if no override is provided.

As example, for the following config:

[indexSearch, { outputDirectory: './public/search'], [feed], [sitemap], [socialImages]

All plugins will create files at ./public/search, instead of creating at each default output directory as the config object is shared between them. It would be necessary to find out how to pass isolated objects and if any additional changes to the structure of the plugins are required.