[D2.4] Add Papyrus icons for Package diagram
[D2.4] Add Papyrus icons for BDD
[Ð2.4] Add IBD Papyrus icons
[D2.4] Add icons for Sequence Diagram
[D2.4] Add icons for requirements
[D2.4] Move Flow spec and Atomic Ports from BDD to IBD

Fix for https://github.com/openETCS/requirements/issues/26