Increases precision of percentages shown in 'Total' bar on the progress page.

The percentages shown currently can be confusing. For example, if the true weight
of a category is 0.76925% and the student scores 100% in it, they will see '0.8%
out of a possible 1.0%'. Increasing the precision to 2 decimal places changes it
to '0.77% of a possible 0.77%'.

LMS-2205
Merge pull request #2784 from edx/usman/lms2205-progress-page-inconsistency

Increases precision of percentages shown in 'Total' bar on progress page