Fixed bug that stores multiple instances of the same tf data in the database; also, maintenance

The thresholds can now be set using parameter flags:
-k: vectorial distance threshold (euclidean distance)
-l: angular distance threshold (angle between two quaternions)
-m: time distance threshold between two transforms

Also, changed internal double variables for threshold management to float as no double precision is necessary here.

The addressed storage-related bug would store in incremental list of transforms per tf message instead of just storing one transform per transform received.

This fixes 3.