Refactoring WOLF installation system

For the time being, wolf plugins are conceived to be installed in /usr/local folder. This forces the user to install it with sudo privilege and makes packaging difficult. To implement modern cmake practice, we may use cmake version >= 3.16 which comes installed with Ubuntu version >=20.

The expected behavior is that you may set a prefix variable (in your .bashrc for instance) that is a path to directory where you want WOLF to be installed. You can then use this variable to set the CMAKE_PREFIX_PATH and CMAKE_INSTALL_PREFIX cmake variables. For instance:

# in your .bashrc  
export WOLF_PREFIX = /absolute/path/to/the/install/location  

# in wolf core/build directory, compile as follows  
cmake .. -DCMAKE_PREFIX_PATH=$WOLF_PREFIX  
make install  # no need for sudo!  

# in wolf IMU plugin imu/build directory
cmake .. -DCMAKE_PREFIX_PATH=$WOLF_PREFIX  -DCMAKE_INSTALL_PREFIX=$WOLF_PREFIX
make