Draft: Helpers 2.1

[Salamandar]

Those helpers (not all are reimplemented) present multiple changes :

• A new underlying library based on bash-modules https://github.com/vlisivka/bash-modules/tree/master/bash-modules with a reworked logging code (it allows stdin and args inputs).
  It contains a lot of helpers, like string::empty, string::contains, array::contains, etc, that reeeaaally help readability.
• A new arguments::parse library from bash-modules, way more competent and readable than the current one
• A new function name schema ynh::<module>::<function>, e.g ynh::systemd::action. For me it kinda helps knowing what a function is about when reading code.
• A lot of the current yunohost code is string-based, even for lists of things. I'm trying here to use more arrays.

This really just is a draft about what could be a future version of the helpers, to have feedback about what it looks like.

Nice examples to read are ynh::fail2ban::add and ynh::setting::get.