Make new emph overlay-aware

Something along the lines of

\newcommand<>{\emph}[1]{\alt#2{\structure{#1}}{#1}}

(I, personally, still would prefer to have another command for this, instead of \emph. In my environment, I have defined \textb{} for Jülich-blue text, and \textbb{} for bold Jülich-blue text. Defined along the lines of above's definition.)