Allow to partially export content

Problem/Motivation

By default all dependencies are fully exported. Sometimes it's a huge export when you just want to export a small piece of content e.g. you already exported all dependencies or you don't need them at the moment, and you just wanted to sync one page instead of all dependencies.

The idea is to add a checkbox to export form and an option to drush command that will allow user to fully or partially export the content.

Probably the easiest way will be to exclude all entity reference fields from the export, so when importing these fields will be untouched.