Add virtual destructors to abstract classes

I added a virtual destructor to all the classes defined in
wholeBodyInterface so that the implementations of these abstract classes
can redefine the destructors.
Implement destructors

Add implementation of destructors in all classes of
wholeBodyInterfaceIcub. The destructors just call the close method.
Merge branch 'issue6'
Improve paramHelp documentation
Merge branch 'master' of https://github.com/robotology/codyco