continuing cleanup: small fixes
continuing cleanup: small fixes

This commit contains the following bug fixes:

* `measure_time` looked for some variables by calling them with the wrong
  name (`later` instead of `end_time` and `now` instead of `init_time`)

* In `main`: `rate` was assigned the wrong value (an extra call to
  `sleep` that shouldn't have been there)

* In `ToFSuspensionController._find_theta`: references to
  `self.req_height` should have been to the `height` argument of the
  method.

* Wheels are no longer indicated by their indices, but by the name of
  their TF transform. This is still very much a temporary solution, and
  not very different from the previous, but it's slightly cleaner.

team-diana/tof_suspension_controller