#164https://github.jpl.nasa.gov/MissionControl/vista/issues/299
App logo and bg files renamed;
Added openmct.scss to hold openmct-specific styles;
Renamed _startup.scss to startup-base.scss
which now renders its own .css file;
Still to-do: apply to WARP including needed
mods to its About dialog screen;
#164
Markup in index.html and about-dialog.html
changed to simplify and use :before/:after psuedos;
CSS in _logo-and-bg.scss modded for same;
Added _startup.scss to hold general CSS for
the startup screen;
Renamed startup.scss to startup-open.scss;
Modified SplashScreenManager.js to target renamed
outer container .l-splash-holder;
Added media query for startup screen on phone;
Cleanup: moved classes out of _effects into _global;
Still to-do: apply to WARP and VISTA, including needed
mods to their About dialog screens;
