[devtools] Add NewCardsScreen and clean up Activities page behavior

[corinagum]

Fix #67
Fix #68
Partial add to #42

• Organize all imports
• Collapse chat nav bar on smaller screens
• Scroll just the table in activities view
• Flex column for Activities view on smaller screens
• Show filter indicator (purple icon) when activities are being filtered
• Keyboard nav for activities grid
• Select activities via radio button
• Add start to new CardScreen using official Adaptive Cards Designer (not hooked up)
• No horizontal scrolling (of entire screen) in Cards view or Activities vew

See Filter icon is changed when filtering is on

Updated Activities view

Smaller screen view

Menu when filtering by id