Add arm and gripper data packets

[sbrokal1]

Update src/data to contain data packets for both arm and gripper. Each has 2 data packets, with appropriate constructor and getter to match all data needs.

[sbrokal1]

Made requested changes.

[Levi-Lesches]

Nice. Now... documentation? 😁 Make each doc comment start with ///, eg,

/// The first data packet sent by the Arm board.
struct ArmPacket1 {
  private:
    /// The current angle of the swivel joint, scaled by 1000 to be a 5-digit integer. 
    unsigned short swivelAngle;

    /// The target angle of the swivel joint, scaled by 1000 to be a 5-digit integer. 
    unsigned short swivelTarget;
    ...
}