Updates to ROS2 support

[gonzalocasas]

Before releasing 2.0, I wanted to clean up, and move some stuff around regarding the ROS2 action support:

• Added wait_goal to wait for an action goal
• Moved actionlib inside roslibpy.ros1 to avoid confusion with having to identically named things in roslibpy and roslibpy.actionlib, so, now usage of ROS1's actionlib is explicit. This is a breaking change.
• Added integration tests for the ROS2 action client
• For ROS2, updated integration launch files to use python instead of XML format.
• PR Fix KeyError in ROS2 ActionClient when receiving action results from rosbridge #142 is also merged into this, so, ideally we review/merge that one first

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I added a line to the CHANGELOG.rst file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke check).
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[gonzalocasas]

@sea-bass @EzraBrooks could you also take a look at this one, pls? thx!

[sea-bass]

LGTM!

As a nitpick, there are many comments throughout this PR that say "ROS2" instead of the preferred styling "ROS 2" with the space. If you'd like to update those, that would be appreciated.

[sea-bass]

I think it's just .Goal in ROS 2

[sea-bass]

Likewise it's just .Request and .Response for services

[gonzalocasas]

I updated the action-related classes to remove the Action prefix at 7c52a8d
For now, if you agree, I would prefer to keep ServiceRequest and ServiceResponse names as they are to minimize the breaking changes.

If that's ok, then I will merge this PR

[gonzalocasas]

LGTM!

As a nitpick, there are many comments throughout this PR that say "ROS2" instead of the preferred styling "ROS 2" with the space. If you'd like to update those, that would be appreciated.

styling fixed at 2c1ee67

[gonzalocasas]

@sea-bass thanks!! merging!