rospy: remove superfluous imports
rospy/roscpp: refactor TopicStatistics message

use Duration where possible. switch from logging variance
to logging standard deviation (stddev), as this better fits
the Duration data type.
roscpp: don't use tabs
rospy: adhere to PEP 8 + cleanup of comments

don't use tabs
rospy: bugfix for issue introduced during refactoring

dividing a rospy.Duration by a float doesn't work as expected.
rospy: make variables configurable through parameters
roscpp: make variables configurable through parameters
rospy: fix a bug that makes window resizing behave badly