Gaze switch node

Using the A button on the joy pad to switch between a topic for gazing (dfault looking at people) and the remote control (means just cancelling the current gaze goal)
Merge branch 'hydro-devel' of https://github.com/cdondrup/strands_hri into hydro-devel
Merge pull request #49 from cdondrup/hydro-devel

Gaze switch node
Merge branch 'hydro-devel' of https://github.com/strands-project/strands_hri into hydro-devel
Merge pull request #50 from marc-hanheide/hydro-devel

created new webservice to make the robot speak
Merge branch 'hydro-devel' of https://github.com/strands-project/strands_hri into hydro-devel
added call to ros_datacentre to make string persistent