Extend image export functionality from component architectures only to task and platform architectures

Description

Extend the functionality defined in eu.fbk.af3.tools.diagram.ui.commands.AbstractComponentToImage.export(String saveFilePath, Component component) to support task and platform architectures as well - ideally through a generic implementation.

Expected behavior

The “Export component as image …” feature shall behave exactly the same as for the component architectures, allowing the export of the architectures with their respective layouts.

(from redmine: issue id 3712, created on 2019-04-15)