Nodelets

Splits monolithic feature node into nodelets:

• downsampler
• pole_extractor
• corner_extractor
• virtual_bumper

Adds test based on playing back bagfile and looking for output at end of pipeline. Reformats/renames files and namespaces to comply with ROS naming standards.

Removes combined topic for corner+pole points - will require another nodelet for this. Still many unused includes.