luci-proto-openvpn: graft app i18n strings into luci-base

luci-proto-openvpn: graft app i18n strings into luci-base

First graft the strings from app -> base
```sh
for dir in $DIRS; do
msgmerge --update --no-fuzzy-matching \
  ${dir/applications\/luci-app-openvpn/modules\/luci-base}/base.po \
  $dir/openvpn.po
done

msgmerge --update --no-fuzzy-matching \
  applications/luci-app-openvpn/po/templates/openvpn.pot \
  modules/luci-base/po/templates/base.pot
```

Then

build/mkbasepot.sh
build/i18n-sync.sh modules/luci-base/

Signed-off-by: Paul Donald <redacted>