Complete work for rendering reports

[bmtcril]

Report rendering using the generate_docs sub-command was never completed. Here are the tasks I believe are necessary to complete this work:

• Package the template files with the distribution so it can be rendered without manually copying files around
• Clean up the use of rendered_report_source_link_prefix. In some places this currently works (ie safe list) but other places (local models) it doesn't (ex: https://github.com/openedx/edx-platform//openedx/edx-platform/common/djangoapps/course_modes/models.py#L971)
• Safelisted models shouldn't have line numbers
• Local model files contain extra path information (ex: /openedx/edx-platform/common/djangoapps/entitlements/models.py) this is part of the problem above
• More labels are needed to explain what the various pages are showing
• Add option to render to HTML as well as RST, this should just creating 5 new templates and a command line option
• Update docs to include this sub-command
• Tidy up the "rendered at" timestamp to be more readable