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.
This requires fixing the javascript api implementation, and adding
an implementation of get_block to the ModuleSystem api.
However, the implementation is incomplete, due to mismatches between
the expectations of XModule and XBlock.
Also adds tests using the Acid block to make sure that the javascript
and python apis for children are working correctly.
I tried to make DictFieldData strict about only being used with one
block. That effort failed ultimately, but these are reasonable changes
I made along the way.
By transparently proxying between the XModuleDescriptor and the XModule,
and between their runtimes, we can make them act as a single class, so
that we can swap in an actual XBlock instead.
