RSS: Change 'New news' to 'News' in announcements

'New news' sounds redundant, and the plugin is known for reannouncing
olf headlines anyway. ;)
RSS: Update translation files
src/conf.py: use ISO 8601 in reply.format.time.

If I read the code for Time correctly, it uses this value by default. I
think that this fixes #701 .
Merge pull request #703 from Mkaysi/time

src/conf.py: use ISO 8601 in reply.format.time.
Merge pull request #626 from nyuszika7h/rss-announce-prefix

RSS: Change 'New news' to 'News' in announcements
RSS: Update l10n-fr.
check_trans.py: Ignore Ctcp and Owner. Closes GH-630.
Update CONTRIBUTING.md to include guideline on internationalization. Closes GH-633.
RSS: update l10n-fi.
Misc: update l10n-fi.