Fix arrow positioning
Fix arrow positioning

- text used to wrap onto two lines but has been shortened, so arrow was hanging down
- implemented flexbox to vertically align arrow and text
- includes a hack for IE10/11 to explicitly set the height, as otherwise vertically centering isn't respected (sorry)
- IE9 and below still don't look perfect

alphagov/collections,alphagov/collections,alphagov/collections,alphagov/collections