Use of markup in .ui strings

Hi all,

Commit 8274df8 seems to have introduced the use of markup in .ui files
to set text in bold, however this is not really a good idea l10n-wise as
it is very error-prone, Gnome is actually moving away from using markup
in translatable strings[1], which I think something LibreOffice should
do. Glade/.ui files support <attributes> which can be used to set text
attributes that affect the while string, while markup is reserved for
the rare case where only part of the string need to be marked up (though
it is still not a very good idea).

Regards,
 Khaled

[1] https://live.gnome.org/GnomeGoals/RemoveMarkupInMessages