[BD-04] Convert ErrorModule and NonStaffErrorModule to XBlocks. [SE-3191]

Converts the Error XModule and NonStaffError XModule into XBlocks.

Part of [XModule to XBlock Conversion work](https://openedx.atlassian.net/wiki/spaces/AC/pages/1472790755/XModule+to+XBlock+Conversion).

*Testing instructions*:

• In a course add a video xblock and an annotatable xmodule ([howto](https://edx.readthedocs.io/projects/edx-partner-course-staff/en/latest/exercises_tools/annotation.html)) and publish them.

• Cherry-pick the second commit in this PR with the message: "Temp code for testing.".

• View the xblock and xmodule in studio and LMS and note the behavior.

• Check out this branch and check the behavior of both in studio and LMS again.

*MRO Analysis*

Descriptor MRO | Module MRO | Block MRO | Notes
------------ | ------------- | ---------------- | ------------
<class 'xmodule.error_module.ErrorDescriptor'> | <class 'xmodule.error_module.ErrorModule'> | <class 'xmodule.error_module.ErrorBlock'>
<class 'xmodule.error_module.ErrorFields'> | <class 'xmodule.error_module.ErrorFields'> | <class 'xmodule.error_module.ErrorFields'>
<class 'xmodule.x_module.XModuleDescriptor'> | |
<class 'xmodule.x_module.XModuleDescriptorToXBlockMixin'> | | <class 'xmodule.x_module.XModuleDescriptorToXBlockMixin'>

1.  

   1.  

      1. Annotatable XModule

In Studio:


In LMS with staff account (component will not be displayed for non-staff accounts):


1.  

   1.  

      1. Video XBlock

In Studio:


In LMS with staff account (component will not be displayed for non-staff accounts):


This does seem to be unexpected behavior but I have left it unchanged.