Feature/accessible completion rate graphs

This gives us nicely formatted completion rate tables like:

|Date of completion (week)|	Completion percentage|
-------------------------|-----------------|
|25 November|	7%|
|2 December	| 8%|
|9 December	|5%|
|16 December	|12%|
|23 December	|12%|
|30 December	|9%|
|6 January 	|0%|
|13 January	|0%|
|20 January	|0%|