Sets fixed ranges on scatter plot coach report.
Shows username if no first or last name for a user in coach reports.
Fixes timeline coach report to only show data for students with sufficient data to plot.
Fixes timeline coach report to only show plot if any students have time line data.
Fixes coach reports to display "Ungrouped" as an option to view exclusively ungrouped students.
Adds control panel link to student coach reports for Ungrouped students.
Fixes nit and spelling.
Fixes wrong variable name in ungrouped_available flagging.
Merge pull request #2234 from rtibbles/coach_report_tweaks

Coach report tweaks