Responsive: small screen fixes

• Center accession image horizontally on small screen
  => Add class justify-content-center on row https://forgemia.inra.fr/urgi-is/gpds/blob/master/frontend/src/app/germplasm-card/germplasm-card.component.html#L159
• Add non breakable space   in result section title (otherwise the: wraps to a new line on small screens)
  => s/Results :/Results :/ https://forgemia.inra.fr/urgi-is/gpds/blob/master/frontend/src/app/result-page/result-page.component.html#L50
• Add space to break text in Acquisition/Creation date (otherwise the text overflows in small screens)
  => s|Acquisition/Creation date|Acquisition / Creation date| https://forgemia.inra.fr/urgi-is/gpds/blob/master/frontend/src/app/germplasm-card/germplasm-card.component.html#L403
• Fix accession image popover placement on small screen. As-is, it overflows to the right of the screen with no possibility to scroll
• Re-layout the trait widget for small screens (might be difficult!)

Example of accession with an image for the above issues: http://urgi.versailles.inra.fr/gpds/germplasm?id=ZG9pOjEwLjE1NDU0LzEuNDkyMTc4NTc1ODc5Mzg1M0UxMg%3D%3D

ping @celia.michotey @jeremy.destin @Melanie.Buy @guillaume.cornut