Milestone 2gb Accessibility of file explorer

[timea-solid]

File Explorer contains more panes and elements, each of which needs to be updated.
IMPORTANT - some panes are only visible once Power User is active.

Part of the file type display:

• Data Content pane
• RDFXML pane
• n3 pane
• humanReadable pane
• source pane
• pad pane
• internal pane
• default pane
  Sharing pane:
• sharing pane
  Schedule
• Schedule pane
  Image pane - visible when an image is uploaded in the explorer
• Image pane
  Folder Pane
• Folder Pane
  Form Pane
• Form Pane

TODO for each:

• adding HTML5 and ARIA labels
• add accessibility tests based on 'axe-core' (example here)
• making sure it also work when resizing screen
• making sure other accessibility features are inline with the WCAG standard (the tests will show). As example: text sizes, button sizes, keyboard focus and so on.