Defaults: header level for Beamer

[cagix]

currently we use a "title" metadata variable and start with H2 headers, which is also "hard wired" in the beamer default file.

we could use the option --shift-heading-level-by=1 to propagate the "title" field to the first H1 header. however, we'd need to use in the document also H1 instead of H2 headers (which will be demoted to H2 with this option). this would need changing in the beamer default file, too.

question: bc uses already H1 to group parts of her larger slide sets. would this still work?