[LMS-1645]
[LMS-2062]
[LMS-2063]
[LMS-2064]

Added feature setting 'DISPLAY_HISTOGRAMS_TO_STAFF' to configure display of histograms in Staff Debug Info panel.

Generating histograms requires scanning the courseware_studentmodule table on
each view. This can make staff access to courseware very slow on large courses.

Default is False.

LMS-1199

Renamed feature setting 'DISPLAY_HISTOGRAMS_TO_STAFF' to 'DISPLAY_DEBUG_INFO_TO_STAFF' to better communicate its purpose.

Default is True.

LMS-1199

Removed inappropriate section tags. Because screen readers announce each section, they should not be used unless they are actually defining meaningful sections.

Make XBlock client-side runtimes proper classes, so that handlerUrl can
be defined in a per-runtime way, and we can have multiple runtimes on a
single page.

[LMS-1630][LMS-1421][LMS-1517]

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]

[LMS-57]

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.

Update existing tests and provide new ones to test new paradigm.

This standardizes the XModule field default values to be the same as the
values that are presented by studio when a component is added to a
course.

Conflicts:

	lms/templates/staff_problem_info.html
	lms/xmodule_namespace.py

made a special 'module preview' view for Static Tabs in the CMS. Per Tom, he'd like just the Display Name to show up in the static tab editor until the end-user clicks the Edit button