* get rid of six.text_type(s)
* get rid of six.b()
* get rid of six.string_types
* get rid of six.PY2/six.PY3
* get rid of six.iteritems() and six.viewvalues()
The XQueueService is used only by the ProblemBlock. Therefore, we are moving
it out of the runtime, and into the ProblemBlock, where it's initialized only
when it's going to be used.
As part of dissolving our sub-projects in edx-platform, we are moving this package under the xmodule directory.
We have fixed all the occurences of import of this package and also fixed all documents related references.
This might break your platform if you have any reference of `import capa` or `from capa import` in your codebase or in any Xblock.
Ref: https://openedx.atlassian.net/browse/BOM-2582
