ros_sql: optional echo SQL to console
Revert "allow strings with null characters to be saved to postgres"

This reverts commit c919a77fb42e97322ed76ea56caa8779fbbe7bca.

This breaks automatic decoding of said fields to python
strings (i.e in resultswebbrowser)
print errors using rospy logerr and show the offending topic
add more (currently failing) tests
bugfix: nested types and prefixes work together now
util.py: add_time_cols(): 'prefix' -> 'name_base'

This usage is not equivalent to the use of 'prefix' elsewhere in
ros_sql, so I renamed this parameter.
util.py: allow single ROS param to set recorded topics
add concept of 'top level columns' e.g. for ROS multimaster
fix crash