tools/i18n: Add support for branch parameters.

One could do other things with this, but what I expect us to do is
pass `-b {branch}`.

tools/i18n/push-translations

@@ -7,4 +7,4 @@ set -e
 set -x
 
 ./manage.py makemessages --locale=en
-tx push -s -r zulip.djangopo,zulip.translationsjson
+tx push -s -r zulip.djangopo,zulip.translationsjson "$@"

tools/i18n/sync-translations

@@ -7,6 +7,6 @@ set -e
 set -x
 
 ./manage.py makemessages --all
-tx pull -a -f --mode=onlytranslated --minimum-perc=5
+tx pull -a -f --mode=onlytranslated --minimum-perc=5 "$@"
 ./manage.py compilemessages
 ./tools/i18n/process-mobile-i18n