Switch button usage per #231
Make more things plottable

This extends the notion of what is plottable to include arrays and
simple message types, in addition to individual fields in messages
imported qDebug in data_plot/__init__.py
Merge pull request #248 from bricerebsamen/patch-1

imported qDebug in data_plot/__init__.py
Merge pull request #246 from trainman419/plot_all_numeric

Make more things plottable
Merge pull request #245 from trainman419/clear_topics

Switch button usage per #231
use TopicStatistics only if available
Merge pull request #252 from ros-visualization/topic_statistic_only_if_available

use TopicStatistics only if available
add missing test dependency on python-mock