Adding seed options to IK Solver Service srv file

Adds new optional field for joint angles seeds to be used by IK
Solver. Also adds seed type mode field for controlling behavior
of seeds used by IK Solver.

Corresponds to change on robot-side S/W in service provider.
Merge pull request #39 from RethinkRobotics/ik_seed_service

Adding seed options to IK Solver Service srv file