Fix: Changes tf message type to tf2.

[matthias-mayr]

We noticed that the MIR is publishing messages in tf2. This is one way that works from us, but one might want to use one of those rewrite functions.

I am not too familiar with this software stack, so I leave it to you.

[mintar]

This is only a cosmetic change. tf.msg.tfMessage and tf2_msgs.msg.TFMessage have the same md5sum, so it doesn't matter which one you publish; if one node publishes tf and another subscibes to tf2, it just works.

I have no objections against switching to tf2, but in that case also the package.xml and tf_remove_child_frames.py should be updated. If you want to add it to this PR, I'll merge it.

[matthias-mayr]

Thanks for the comments. They were exactly the type of comment I wanted to have on this PR.

I removed the change of the tf message include and added only the additional subscription that is necessary to get a full tf tree.

[mintar]

Ah, I hadn't seen that part of the PR. Yes, adding tf_static is of course necessary. Thanks for the fix!