The SensorPtr types have changed from boost:: pointers
to std:: pointers,
which requires boost::dynamic_pointer_cast to change to
std::dynamic_pointer_cast.
A helper macro is added that adds a `using` statement
corresponding to the correct type of dynamic_pointer_cast.
This macro should be narrowly scoped to protect
other code.

Some boost headers were remove from gazebo7 header files
and gazebo_ros_joint_state_publisher.cpp was using it
implicitly.

In gazebo7, the rendering::Camera::SetHFOV function
is overloaded with a potential for ambiguity,
as reported in the following issue:
https://bitbucket.org/osrf/gazebo/issues/1830
This fixes the build by explicitly defining the
Angle type.

Make sure to include gazebo_config.h,
which defines the GAZEBO_MAJOR_VERSION macro