fix(premeeting): Improve pre-meeting responsiveness for screens less than 1000px
fix(premeeting): Improve pre-meeting responsiveness for screens less than 1000px

Use 720 (HD) width as breakpoint to change screen layout
Reduce join panel size to be able to see video camera pic

jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet,jitsi/jitsi-meet,jitsi/jitsi-meet,gpolitis/jitsi-meet