Deal with dependencies when deleting a module version

[fmeurisse]

There are 2 solutions to resolve this problem:

• We can cascade the deletion on the @onetomany relationship between ModuleVersion and Dependency list
• or delete the dependencies before deleting the ModuleVersion

Since a dependency can not exists without a ModuleVersion I think is better to use the cascade solution.

[FroMage]

Done by asking the user to delete the dependent modules.