Use enum instead of int in TextMetrics::getAlign

This is just a code cleanup, no (intented) effect.
Revert "AGUTeX template/layout: support the new cls name"

This reverts commit cde8707 and changes "AGUTeX" back to "agutex".
The maintainer has changed "AGUTeX.cls" back to "agutex.cls" and has
confirmed (through private email) that he plans to keep the filename
all lowercase now that he is aware of case-sensitive file systems.
Improve parsing of ERT arguments in beamer block titles.

Fixes: #9225