Date separator style was just define don any h2 in the message
list, so got picked up by any h2s in markdown too. Give date
separators their own class.
Fixes https://github.com/vector-im/riot-web/issues/4328
Also, make sure the typing avatars line up with the arrow to jump to the bottom of the timeline.
Also, get rid of any height jumps when a call starts. border 1px hidden does not add any height to an element, it is effectively the same as none.
This will ensure that errors, unsent messages, etc. will be allowed enough height to display their contents from within the status bar without being chopped.
Fixes#3041
SVGs are all broken, and some of the more exotic colours haven't been updated. There's been no attempt to use SASS to remove duplication from the CSS yet.
no attempt to switch it at runtime yet.
