Update list of letters

[gspinaci]

Remove the header part of the letters page. The text is mostly redundant. We should have something like the screenshot (with less padding on the bottom).

The columns should be the following:

• Image (without the image label) & The letter number below without the leading "0"
• Letter (the current content we have in this column)
• Summary (here we should have the content from the spreadsheet names "Letters Contents"
  -Subjects (not clickable)
• Location (If there is room here)