Refactor existing plugins

[xela-95]

This issue keeps track of the refactorings that should be applied to the existent plugins of this repo in order to conform to the coding conventions used by the new ones (e.g. basestate).

List of modifications:

• [ ] In the CMakeLists.txt file of the plugin, remove ${YARP_LIBRARIES} env. variable in favor of proper targets (e.g. YARP::YARP_dev and/or YARP::YARP_sig) https://github.com/robotology/gz-sim-yarp-plugins/pull/70/files/0d99d7e665ba4784e9c0aac8380e4eae89ab4d4c#r1466436549
• [ ] Remove useless project() invocations
• [ ] Use RAII to delegate the management of the yarp network instead of doing this manually https://github.com/robotology/gz-sim-yarp-plugins/pull/65#discussion_r1466093438
• [ ] Avoid that clang-format produces ugly code formatting for too long statements. Solutions are to define aliases with long types or locally disable clang-format with https://clang.llvm.org/docs/ClangFormatStyleOptions.html#disabling-formatting-on-a-piece-of-code
• [ ] Always use curly brackets for if else statements
• [ ] Always enclose lock_guard in a dedicated scope
• [ ] Rename the plugin singleton data members to meaningful names (see basestate plugin)
• [ ] Assign pointers to nullptr instead of NULL
• [ ] Remove from the README in plugin tutorial the section to address to WSLg issues, see https://github.com/robotology/gz-sim-yarp-plugins/issues/40
• [ ] Format every source file to have a EOL at the end of the file
• [ ] Uniform namespace (e.g. no different namespace for Gazebo and yarp classes of the same plugin)
• [ ] Adopt IWYU
• [ ] Uniform gzyarp namespace

[xela-95]

CC @traversaro feel free to add other points if I missed something.

[traversaro]

Perfect!