Add options to toggle odom and alias tf (continued from #92)

[willcbaker]

See #92

This feature introduces parameters to toggle on/off publishing of TFs to avoid tf conflicts from other sources.

For examples:

if this were used as an odometry signal in http://wiki.ros.org/robot_localization you need to toggle off the odom->base_link tf
if not using base link frame_id but the tf already exists (e.g. from robot_state_publisher) do not publish an identity transform

[willcbaker]

clean whitespace

[sumanthrao1997]

Thanks for this commit, it was useful to me.

[nachovizzo]

@willcbaker would you mind giving me access to your branch so I can directly make the changes there?