Published libraries imported by reference are editable if they contain no LibraryPackages

[flatombe]

To reproduce:

• Create a SysML project with a Package as root element, and publish it
• Import it "by-reference" in another project.
• => The corresponding resource is displayed at the root of the tree (this is intended) but its contents are editable. This seems counter-intuitive since any changes to it will be replaced whenever we get the chance (i.e. by closing the project 6 seconds and re-opening it).

Note that this does not happen if the published library contains at least 1 LibraryPackage, e.g.:

• Create a SysML project with a Package and a LibraryPackage as its root elements
• Import it "by-reference" in another project.
• => The corresponding resource is now displayed under "User libraries" (because it contains at least 1 LibraryPackage) and its contents are read-only.

Suggested fix:

• Resources from imported-by-reference libraries, even without a LibraryPackage, should be read-only
• OR their modifications allowed but upon changes to it we should open a dialog to switch the dependency from "by-reference" to "by-copy" (which is actually more of a "local fork" of the published library).