refactor(webserver): migrate remaining table/iframe attributes to CSS - #99

Finish the presentational-HTML migration started in amule-project#95. That commit
covered background=/bgcolor=/align=/valign=/border= and the body
margins; this one retires what was left, keeping the quirks mode
doctype untouched so the table layout renders exactly as before:

- cellspacing= / cellpadding= are dropped from every table. A global
  `table { border-spacing: 0 }` plus `padding: 0` on the existing
  th/td rules covers the 0/0 case used almost everywhere; the three
  exceptions get spacing1 (login box frame), spacing6 (prefs and Kad
  toolbars) and pad4 (search form) classes. pad4 uses a
  `> tbody > tr > td` child selector so it matches the cellpadding
  semantics of styling only the table's own cells.
- width= on td/th (deprecated since HTML 4.01) and width=/height= on
  table (height was never valid HTML, it works via quirks mode)
  become w*/h* utility classes next to the existing h10..h200 set,
  with a `p` suffix for percentages (w50p, h100p, ...).
- frameborder="0" and width="100%" on the footer/stats/stats_tree
  iframes become `iframe.noborder` and w100p classes. The two log.php
  iframes keep their default border as today (they never set
  frameborder), so they only get w100p.
- scrolling="no" (obsolete, no CSS equivalent on the iframe element)
  is replaced by `overflow: hidden` on the body of the two framed
  documents themselves, footer.php and stats.php (body.frame).

Pixel heights on img and iframe stay as attributes - they are valid,
non-presentational HTML.

Verified against a running amuleweb: before/after headless-Chromium
screenshots of all 9 pages plus the two footer frames are
pixel-identical except for dynamic content (stats graphs, uptime,
server user/file counts).