General improvements [Frontend]

[SilviaAmAm]

Things that were noticed while working on maykinmedia/open-archiefbeheer#54

• The component AttributeTable does not wrap on mobile view
• In the DataGrid component, if there are few rows and the paginator is used, the paginator is shown under the last row of the table. It would be nice to be able to show it at the bottom of the page like in this design
  
• When the component DataGrid is loading, the spinner is shown on the paginator (very small). I hadn't noticed it at all in the beginning, so I think the 'loading' state needs to be clearer. It should also not be possible to select/deselect items while data is being fetched.
• In the DataGrid component with filters, for every keystroke a request is sent to the backend. This should probably be debounced.