Careful identification of "dashboards"

@mhoeber , this is just cleanup. This came out of the issue that Alison Kuryla's course team had finding "dashboard" in the docs. The JIRA item in the name is for any changes for course re-run to the "My Courses" dashboard, and pointed at 2. There aren't any visible changes, so I spent a half hour going through and identifying the various dashboards in text for Alison instead. And found a couple missed "New Beta Instructor Dashboard" references too -- yuck!