Milestone 2ga Consolidate CSS 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:

• extracting all inline CSS in dedicated CSS files (example in profile-pane) Very important is to create dedicated CSS pane names. Example: if you use the .warning, its CSS will be coming from mash.css so create a dedicated .warning-contact for it if the one in mash.css does not fit.
• making sure the CSS is part of the release. Maybe we need a webpack) build, and an accompanying entry file (example index.ts)
• using already available CSS variables from mashlib light theme and documenting in the PR what other CSS variables could be moved to the main mashlib theme