add dummy strings

To get all dates localized, we need all runtimes to have the i18n
service, and since runtimes are made by the modulestores, we need to
pass it to them.

Soon (fingers crossed), modulestores won't be involved in making
runtimes, and many of these changes will go away.

update strings

make openendedchild and open_ended_module_v1 act enough like xblocks to get xblock 18n

We use pybabel to extract strings from third-party apps, put them on
Transifex, then merge them into django.po.

[LMS-1681]

LMS-1967

Use the configuration more, and we don't need to delete files we're
about to create.

Messages can be segmented into different .po files based on the location
of their occurrences.  This is so Studio strings can go into different
.po files so we can direct Transifex workers to the LMS strings we
really need done.

both tests work

ran tests successfully with
$cd i18n; python -m unittest test