TableCell Text Styling

[natalynyu]

This PR adds text styling to the contents within a table cell. The medium and negative text colors in the theme were updated per accessibility (color contrast) recommendations from Vittorio in ticket #300. I added an optional variant property to the TableCell so that users can use the VARIANT.MEDIUM (which we will use for "No Longer Active" faculty absence fields in Course Planner) styling and VARIANT.NEGATIVE (which we will use for other faculty absences that need attention in Course Planner) styling. If the user does not specify a variant, the text font-weight and color will default to the theme's base color and medium weight, which is how all table cells were styled originally before this ticket.

Describe your changes

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have run eslint on the code
• [x] I have added JSDoc for all of my code (where applicable)
• [x] I have added tests to cover my changes.

Priority:

• [x] Normal
• [ ] High

Related Issues:

Fixes #300

[natalynyu]

@jonseitz sure thing! I updated the TableRow background and hover color through ce93c80.