[enh] New helpers for equivs use
[enh] New helpers for equivs use

- `ynh_package_remove` and `ynh_package_autoremove` were just moved up.
- Small modifications on `ynh_package_install_from_equivs`. Just added some comments and used popd instead of cd.
- Added `ynh_app_dependencies` to manage easily installation of dependencies with equivs
- And `ynh_remove_app_dependencies` to remove them.
YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/yunohost,YunoHost/moulinette-yunohost,YunoHost/moulinette-yunohost,YunoHost/yunohost,YunoHost/yunohost,YunoHost/yunohost,YunoHost/moulinette-yunohost