Introduce new secure setting for the base url of the icommons api since the user and pass are tied to an instance.  Convert lecture video tool and icommons_common settings block to use this new api_host setting and also move them to base since settings are identical or very across environments.  For the canvas_url part of the common block, override the canvas url per environment (defaults to canvas.icommons.harvard.edu).
Merge pull request #139 from Harvard-University-iCommons/feature/modify_api_urls_to_be_consisten_across_environments

Introduce new secure setting for the base url of the icommons api since ...