ptu action server assume too high speed when set to 0

[cdondrup]

When the tile or pan speed are left at 0 the PTU action server seems to assume a high velocity which the motors cannot reach. Therefore the PTU miscalibrates.

Also, it might be nice to enforce limits: tilt 43 - -43 and pan 180 - -180.

[cburbridge]

The maximum/default velocities can be capped with parameters:
https://github.com/strands-project/scitos_apps/blob/hydro-devel/scitos_ptu/scripts/flir_ptu_action_server.py#L20
but it looks like they are only obeyed if there is no velocity given. These parameters should be renamed or made to work as their names suggest.
The limits will be an easy and sensible addition, and should be parameters too.