Implements feature 4 in Shuqun's feature requests. Depends on #427.
On creating an assessment question, a UI for adding variable numbers of keyword-score pairs will be shown.
When the question is graded, the keyword-score pairs for it are shown. The keywords will also be highlighted in the submitted solution, and a grade will be filled in based on how many keywords are present.
Implements feature 4 in Shuqun's feature requests. Depends on #427.