Make messages translatable too

[Steffen Hoffmann]

This plugin has basic i18n for the web-UI, but we should work towards translated announcements as well.

And because there is no Request object on sent time, that could tell about user language preferences, this has to be configured in user settings beforehand.

[Steffen Hoffmann]

(In [12312]) TracAnnouncer: Update AccountManagerPlugin messaging support, refs #7759, #7977, #8740, #8927, #9090 and #9204.

This long-standing regression is fixed now, while associated message templates are rather bare-bone ones yet and formatting could be improved significantly.

[Steffen Hoffmann]

(In [12325]) TracAnnouncer: Fix generator, that was broken by [12309], refs #7759, #7976, #7977, #8740, #8927, #9090 and #9204.

And the same bad filter code even got replicated in [12312]. Sorry for not checking compiler errors earlier. Finally I discovered an UnboundLocalError for resource_id hidden behind the first error. Obviously unit tests are a blessing and needed here too.

[Steffen Hoffmann]

(In [12331]) TracAnnouncer: Really fix filter now, refs #7759, #7976, #7977, #8740, #8927, #9090 and #9204.

Complete the change from [12325] to get expected behavior, or filters would be applied undesirably.

[Steffen Hoffmann]

(In [12342]) TracAnnouncer: Add 'acct_mgr' as default for 'filter_exception_realms' option, refs #7759, #7976, #7977, #8740, #8927, #9090 and #9204.

IMHO this is required for better plugin usability, making AccountManagerPlugin notifications pass without additional configuration effort now.

Some Python doc-string tweaks and another unit test slipped in here too.

[Ryan J Ollos]

(In [12353]) Refs #7759, #7976, #7977, #8740, #8927, #9090 and #9204: Fixed minor syntax error introduced in [12342].