core: automatic width for entities dropdowns

Refs #2314

Prehistoric browsers don't display correctly dropdowns when entities are
very long, so width of select tags is now automatic.
dyngroup: IHM improvement: invert arrows

Refs #2315
core: add word-wrap property for very long menus

Refs #2316
base: IHM Improvement: invert user secondary group lists

Refs #2318
base: Invert arrows for user groups

Refs #2318
dyngroup: Invert arrows in shared group form

Refs #2318