Catkinized, works on Hydro, mostly for ClamArm

I have put a lot of work into maintaining this C++ version of dynamixel_hardware_interface, and it currently builds on Hydro with catkin. Before merging there are a few ClamArm-specific issues, doing a grep:

```
./dynamixel_hardware_interface/include/dynamixel_hardware_interface/dynamixel_io.h:39:#include <clam/gearbox/flexiport/port.h>
./dynamixel_hardware_interface/src/serial_proxy.cpp:15:#include <clam/gearbox/flexiport/flexiport.h>
./dynamixel_hardware_interface/src/dynamixel_io.cpp:39:#include <clam/gearbox/flexiport/flexiport.h>
./dynamixel_hardware_interface/package.xml:11:  <url type="website">http://correll.cs.colorado.edu/clam/</url>
./dynamixel_hardware_interface/package.xml:12:  <url type="repository">https://github.com/davetcoleman/clam</url>
./dynamixel_hardware_interface/package.xml:13:  <url type="bugtracker">https://github.com/davetcoleman/clam/issues</url>
```

But that seems easy to fix. The big issue that I'm hoping to fix is that linking to flexiport using catkin is currently not working. Instead, I have to use the command:
```
sudo ln -s /home/dave/ros/ws_clam/devel/lib/libflexiport.so /usr/lib/libflexiport.so
```
Please help me understand why - I want to learn! I believe this issue is in this [CMakeLists.txt](https://github.com/davetcoleman/dynamixel_motor_experimental/blob/master/dynamixel_hardware_interface/CMakeLists.txt)

Thanks!