Update Roadmap for Humble

[audrow]

The current Humble roadmap, as decided by the ROS 2 team.

[fujitatomoya]

@audrow if we(contributors) would like to add roadmap or task for Humble, we could create PR after this PR? I am thinking that ContentFilteredTopic Feature could be one of roadmap.

CC: @wjwwood @clalancette

[audrow]

Good point, @fujitatomoya. I've added a table for community contributions to the PR. I made the community contributions table separate from the table of contributions we plan to work on at Open Robotics to make it easier for us at Open Robotics to keep track of the tasks we're working on. Also, the Open Robotics table has its items prioritized (so we know what to work on first), which I don't think makes as much sense to do for the community contributions table, as most of the items will have different owners.

[clalancette]

After discussing this with some people, I think we should just consolidate this all down into a "Humble Roadmap". That is, no separation between the Open Robotics Contributions and the Community Contributions. That means we'll also add back the "Owner" column to the table, so that we can track where each contribution is coming from.

Overall, I think this is better because it shows the community what can be expected in Humble, regardless of where that contribution is coming from.

[clalancette]

I just rebased this and added in an expected completion time for the default DDS selection. With that, this looks good so I'll approve. Thanks @audrow !