* Override default slide size by size from master slide or slide
  settings. (What to do if sizes of slide and its master do not match?
  If it can happen?)

* Handle sticky notes on master pages too.

* Set text formatting defaults.

* Figure out how section-style-default is used. For now I assume that a
  section style that does not have a parent is derived from
  section-style-default. But maybe the default style is implicitly used if
  a property in a regular style is empty or missing...

* More TODO items are sprinkled over the source files...