Get l10n within NewUserMailHelper to ensure it always uses the new user's language.
Some related tests had to be changed because they relied on internals, see also from the PHPUnit documentation:
"Exercise caution when using [the at] matcher as it can lead to brittle tests which are too closely tied to specific implementation details."
Signed-off-by: Zulan <git@zulan.net>
* currently there are two ways to access default values:
OCP\Defaults or OC_Defaults (which is extended by
OCA\Theming\ThemingDefaults)
* our code used a mixture of both of them, which made
it hard to work on theme values
* this extended the public interface with the missing
methods and uses them everywhere to only rely on the
public interface
Signed-off-by: Morris Jobke <hey@morrisjobke.de>