Bug #1765276: Upgrading to bootstrap 4.3.1 from 4.2.1

Replaces raw/scss/lib/ files and the lib/bootstrap/assets/javascripts with the new ones
Involved adding some more variables to the bootstrap_variabes file

behatnotneeded

Change-Id: I0440edcbdf53e8ff3994d2e52ce123a2df9ce182