Layout skeleton if JointTrajectoryController.
Add basic trajectory interface and utilities.

- Implementation of single-dof quintic spline segment.

- Multi-dof segment templated on the single-dof segment type.

- General(ish) representation of trajectories, templated on segment type.
Initialize segments with start and end times.

Before the segment duration was provided and zero start time was assumed.
Now initializing and sampling segments have a more consistent API:
- You initialize a segment from start and end time-state pairs.
- You sample a segment with a time[in] and a state[out].
Add doc configuration file.
Add unit tests for segment sampling classes.
First trajectory interface functions with tests.

- Find the segment associated to a specified time instant.
- Sample a trajectory at a specified time instant.
Doc fixes.
Remove dead code.
Test trajectories with overlapping segments.

Excercise the case when a segment's end_time is greater than the next segment's
start_time.
Trivial doc fix.
Harmonize MultiDofSegment constructor signature.

Segment implementations should have a similar way to be constructed, namely
by specifying four parameters:

  start_time, start_state, end_time, end_state

The types of these parameters depends on the segment type, but the structure
is preserved.
Add a non-iterator based findSegment(...) overload.

Used for convenience purposes.
Add utilities for reading trajectories from ROS msgs.
Move trajectory_interface to a separate directory.

General-purpose trajectory_interface functionality should live in a separate
place (ie. ROS package) than the joint_trajectory_controller. This is a first
step towards this separation.
Restructure error reporting log statements.
Scope init method as protected.
Add new trajectory segment type.

- Multi-dof quintic spline segment that can be constructed from ROS message
  data structures.
Implement trajectory init from ROS message data.

Update unit tests accordingly.
Documentation and log message fixes.
findSegment overload returning non-const iterator.