rqt_plot) plot elements in an array at once

[130s]

Once topic is given, the name of elements in that topics become the attributes on the plotter graph.

It would be useful for relatively complicated topic type (eg. IMG, NavSatFix), although with those that have many elements (eg. Pointcloud) the resulting plot might get too messy.

Discussed here.

[130s]

Closing. Although what I originally tried to say is now not clear to me now, #106 will realize that.