Port styling for ReactCSSTransitionGroup animations to style.ts
Avoid class name repetition when defining pseduo and descendant selectors

Change the logic which produces CSS selector names from nested
property names such that:

propA: {
  propB: {
    ...
  }
}

Produces '.propA-propB' if 'propB' starts with a lower-case
letter or '.propApropB' otherwise. This allows pseduo-selectors to
be defined with:

propA: {
  '::pseudo-selector-name': {
    ...
  }
}

And descendant selectors or other non-class selectors in a similar way.
Remove LESS dependency

Make app.less a simple CSS file for the base CSS used by
the web UI and use style.ts for everything else.

Also speed up CSS build a fraction by running autoprefixer
only once on the final CSS file instead of twice (once on
app.css, once on the theme)