HTTP Module: improve handling of page length and responsive design

[onkelandy]

There are still some (known) issues:

• If webif_pagelength in module/plugin is not set to 0, it won't be possible to change to automatic resizing.
• Sometimes responsive behaviour (+ sign) is not predictable, esp. on reload and/or tab change
• Clicking on a responsive + to expand automatically changes the page length back to "Auto"

[onkelandy]

At least "Clicking on a responsive + to expand automatically changes the page length back to "Auto"" doesn't happen anymore. However, as soon as the page gets resized it automatically switches to the "auto" pagelength. No idea if that can ever be fixed.

[onkelandy]

All issues should be fixed with #564