feat(a11y): Globally improve accessibility for screen reader users

- tooltip was reopening in an inconsistent state(without the tooltip text visible), taking the focus from the reactions popup
- removed duplicate store prop from ReactionsMenuButton

Create Tooltip component
Fix Popover positioning calculations
Add margins to popover
Remove @atlaskit/tooltip
Update all components to use the new Tooltip component

Added tooltip actions and reducers for the following functionality: when a user hovers over an element is sees the tooltip for that element and then hovers another element that has a tooltip, instead of using the delay and animations we just unmount the current tooltip and mount the next one immediately