#1250: Add patterns to Resource Access visualizations

[jaydonkrooss]

Added new visual indicators on resource access page to address accessibility concerns: https://github.com/tl-its-umich-edu/my-learning-analytics/issues/1250

• "Resources Accessed" bars retain the same secondary color from palette settings (blue), with the addition of small white squares as a dotted pattern EDIT: not necessary, as the solid pattern will be distinguishable with the stripes
• "Resources Not Accessed" bars retain the same negative color from the palette settings (gray), with the addition of diagonal black stripes
• Patterns are visually distinct with compliant contrast ratios according to WCAG 2.1 https://www.w3.org/TR/WCAG21/#non-text-contrast

[pushyamig]

Overall this is functional as expected