Enable parent/child tests using the acid XBlock.

Also fix those tests to correctly wait until the ajax portions have
finished before evaluating the page contents.
Add block.name to xblock javascript frontend
Add block type to the available attributes in the xblock javascript frontend
Set xmodule_runtime on all XModule-like things (including pure XBlocks using the XModuleMixin)

Expose xmodule_runtime as .runtime if it's set (otherwise, fall back to
the supplied runtime). This causes all blocks to act like XModules when
they have a ModuleSystem, and like XModuleDescriptors if they only have
a DescriptorSystem.
Escape xblock wrapper data attributes and css classes for safe html