ox-beamer.el: Update BEAMER_HEADER placement
* lisp/ox-beamer.el (`beamer-header'): Move BEAMER_HEADER injection to
final part of preamble (after themes, title, etc.). Allows for
custom short titles, etc., with #+BEAMER_HEADER:
\title[Short]{Long}.
* doc/org.texi: Updated BEAMER_HEADER entry with a relevant footnote.
Previously, TITLE, etc., was being injected after BEAMER_HEADER, so
short titles (and related) could not be added. BEAMER_HEADER now
serves as a final preamble injection point.
TINYCHANGE