Create a joint_trajectory_controller rqt plugin.

Initial plugin features:
- Allows to select any _running_ joint trajectory controller from any active
  controller manager.

- Two modes:
  - Monitor: Joint display shows actual positions of controller joints
  - Control: Joint display sends controller commands

- Max joint speed is read from the URDF, but can be scaled down for safety.
Minor fixes

- Sort comboboxes
- More compact _is_permutation implementation
PEP-8 compliance.
Small refactor.

- Move some code to controller_manager_msgs.utils

- Move update_combo to a separate file
Add TODO item.
Use single quotes for string literals. Everywhere.
setValue() doesn't emit valueChanged() if same val
Merge branch 'rqt-jtc' into testing_velocity_controller_indigo