add toggleCardVisibility action

Feature Merge Request

Related Issue

resolves #280 (closed)

either THIS or !230 (merged) is to be merged

Description of Feature

• insert if condition in AssessmentList component to route "Available" cards to new component (see next point)
• create new stateful component (within AssessmentFilterView folder), AssessmentListTabbed, with activeTab property in its own component state -- clicking hidden or unhidden makes that the activeTab.
• AssessmentListTabbed filters assessments according to hidden property (true = 'hidden', false = 'unhidden') and renders only those assessment cards, according to activeTab
• create toggleCardVisibility function in actions/assessmentActions to update card's hidden boolean property in Redux store -- by dispatching UPDATE_ASSESSMENT_VARIABLE action type -- and to toggle UI button text (on assessment card) between 'hide' and 'unhide'
• change AssessmentCard component into connected component -- mapDispatchToProps connects toggleCardVisibility function

What's Next?

• decide if this implementation is ideal, flexible, scalable
• modify assessment card UI according to AssessmentFilterView section? (e.g., 'Current' and 'Completed' assessment cards may not need the 'hide'-'unhide' button)

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