Squashed 'beamerthemes/' changes from 177a717..0346ea1 ...

0346ea1 • Widened side boxes in footer line to fit longer dates (e.g., September).

git-subtree-dir: beamerthemes
git-subtree-split: 0346ea1

Squashed 'beamerthemes/' changes from 2d36aa0..177a717 ...

177a717 • Added Otago “plain” theme.

git-subtree-dir: beamerthemes
git-subtree-split: 177a717