StarUML v3 support

Added support to StarUML v3

Support to multiple linked diagrams

Added basic support to multiple linked diagrams

Fixed a bug that won't let the user navigate to a linked diagram sometimes

When a user added a diagram directly to an element of another diagram, he wasn't able to navigate to it.

UI changes and explorer navigation

Changed toasts color and added also the navigation inside the Explorer view

First release

First release of this StarUML extension that lets you navigate to a diagram linked to an element (if present).