Better log handling for student activity section

[clpetersonucf]

• The student activity section will populate if ANY logs are available for a given instance, not just completed logs.
• The distribution graph renders a warning message instead of summary content if no completed logs are available.
• The Individual Scores tab renders a warning message instead of an error message if no logs are available (for example, if no logs are visible due to provisional access.)
• The Export Options dialog renders an error message if the associated endpoint returns a non-200 error code, and specifically indicates that no logs are available if the response method is 404.

[FrenjaminBanklin]

Provides better feedback in cases where there's nothing to report. Only one nitpick that's not really worth holding this up, otherwise looks good to me.