[trajectory] Add waist signal + squash several commits.

Fix waist, add debug + rational for message handling.
 - waist type is now MatrixHomogeneous and not ml::Vector anymore.
 - add traces
 - messages are better handled based on timestamped and seq id.

trajectory.cpp is not a plugin.

Fix warnings in fir-filter.
Add trajectory initialization through command.

This makes sure that the entity joint-trajectory-command has always
something to provide at the starting point.

This commit introduces boost:regex in sot-core.