Using the XBlock i18n Service for ORA2

And thusly, we use the i18n Service. 

@wedaly @gradyward 

FYI @sarina we're picking up the i18n service in ORA2.
Technically, you also don't need the `u` within `_()` if `_` represents `ugettext`, as `ugettext` is the unicode version of the gettext function and thus always returns a unicode object. However, if the runtime was dumb and just provided gettext instead of ugettext, it wouldn't necessarily return a unicode object. So I haven't made any comment about removing the u from `_(u"blah")` because it just seems like safe / defensive programming.