Hide install deprecation warnings

[VGPReys]

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In this PR, deprecation warning that are printed to user while running the command python3 setup.py develop --no-deps during the installation are silenced.
This is performed by the importation of the warning library and the two EasyInstallDeprecationWarning and SetuptoolsDeprecationWarning warning class from the setuptools library.

To compensate (and somehow remember) that these warnings exists, one line is added in the docs/INSTALL.md to justify the use of python setup.py.

(also related to #617)