Fix new frontend

[xdvom03]

• Properly place explainer windows
• Get rid of the last vestiges of the multi-window system
• Fix TBD as marked in code (i.e. make the overall four cells of the whole window (return to main, current screen, explainers, log) built in less awkwardly)
• Make the four sections more visually distinct
• Return to the proper place (e.g. from list of links in class to the database, not the main menu)
• Test a lot

[xdvom03]

Add to that the occasional overflow of widgets out of the display (mostly caused by a giant comment)

[xdvom03]

State of the union:

• Properly place explainer windows
  • Still popups, no obvious other place to put them, overriding the screen seems unhelpful
• Get rid of the last vestiges of the multi-window system
  • Superseded by #43
• Fix TBD as marked in code (i.e. make the overall four cells of the whole window (return to main, current screen, explainers, log) built in less awkwardly)
  • Fixed by separate frames
• Make the four sections more visually distinct
  • Partially fixed by the canvas substitution for frames, as canvases have visible (but unobtrusive) borders
• Return to the proper place (e.g. from list of links in class to the database, not the main menu)
  • :(
• Test a lot
  • System appears stable now, no forgotten widgets except for the still misbehaving #21

[xdvom03]

Consider the issue limited to: Return to the database when applicable.

[xdvom03]

Superseded by #55.