Add snapshot system

[JaydenGrubb1]

Added a snapshot utility vinca-snapshot for capturing the current version of specified ROS packages. This snapshot can then be used when generating recipes via -z/--snapshot PATH.

[Tobias-Fischer]

Hi @JaydenGrubb1 - thanks a lot for this! When creating the snapshot, can you please change the functionality such that versions are captured for ALL packages in the rosdistro?

[JaydenGrubb1]

Updated to snapshot all packages in the rosdistro.

[Tobias-Fischer]

Hi @wolfv / @traversaro - do you have time to review? @JaydenGrubb1 is just finishing a project with me, and this + #64 are his main deliverables.

[traversaro]

Thanks! Just a non-blocking comment, how does it work if a package is present in the new distro but not in the snapshot? It silently tries to build the latest version?

[JaydenGrubb1]

Your right. As is, it would just try to build the latest version. I guess the correct behaviour would be to skip the package instead?

[traversaro]

Your right. As is, it would just try to build the latest version. I guess the correct behaviour would be to skip the package instead?

I guess so? From what I understand the goal of this feature is to easily rebuild the packages with updated dependencies and fixes, without having to deal with regression due to new versions released. In that context, trying to release new packages could create problems.