* remove Plugins and CloudIntegrations tab and add ConnectData tab
* ConnectData: add Search component and use it
* ConnectData: add DataSourcePluginList component
* add CardGrid component
* add CategoryHeader component
* ConnectData: restructure content
DataSourcePluginList is removed, because its responsibilities are
actually the same as ConnectData's responsibilities.
NoResults was added as a reusable component, and was moved out of
CardGrid, since there could be more CardGrid on one page, but only one
NoResults.
* fix spacer
* use LoadingPlaceholder
* CardGrid: add margin
* generalize CardGridProps
* move isLoading and error into CardGrid
We'd like CardGrid to be reusable, even multiple times within a page.
In this case, it's better UX if we show the loading or error states per
card grid, not for the whole page.
* ConnectData: fix NoResults condition
* fix and add meaningful tests
* fix indentation
* move isLoading and error back to ConnectData
* make `url` required for CardGrid items
