bootstrap4-modules-2.5.3

Update to Bootstrap 4.5.3
Add new skin for alerts
Add some aria info on language menu
Fix language switch menu (add missing mainResourceNode declaration)
Move Jahia-Module-Priority part to the maven-bundle-plugin instructions
#14 Add new class language-nav to be able to customize the rendering of the language menu
#20 Allow to limit the number of items on grid & layout component