Checked the validity of the Connection shared pointer
Changed singleton library to gazebo_singleton to avoid conflicts when installing
Changed namespace (where possible) to `GazeboYarpPlugins`.

In C++ no real naming convention exists for namespace names. I decided to adopt the same convention used for classes (as is used for example in WebKit project).
Renamed GazeboPluginHandler to Handler because now the fully qualified name is not ambiguous.
Renamed (again) singleton library to gazebo_yarp_singleton
the PROJECT() command already assign its argument to the PROJECT_NAME variable

Check http://www.cmake.org/Wiki/CMake_Useful_Variables
Added first version of JointSensors plugin
added missing JointSensors files
Fix crash when removing gazebo_controlboard by properly detaching controlboard from wrapper
Merge branch 'fix/model_removal_crash' into development
Fixed creation of empty shared_ptr
Added proper wrapper detaching for solving issue #58
Merge pull request #77 from robotology/jointgenericsensors

Merge jointgenericsensors in development
Added proper handling of missing yarpserver and robust plugin closing
Test against gazebo3-prerelease
Restore testing against base gazebo
Documentation added
Merge branch 'master' into development
Merge pull request #78 from robotology/development

Adding JointSensors plugin to master for proper simulation of speed and joint torques in coman