Fix: Allow scrolling for #contentForm (skin.css)

[IgorA100]

This will affect many pages, for example:
stats, zones, bandwidth, onvifprobe, add_monitors, export, controlcap, privacy, monitorprobe, monitors, filter, monitor, user
I checked all these pages and they did not get worse.

But pages like "add_monitors", "export", "monitor" require additional layout correction for relatively narrow screens.
Perhaps it is worth reviewing from
"/skins/classic/css/base/views/add_monitors.css"

#contentForm {
  height: 100%;
}

&&
"web/skins/classic/css/base/views/user.css"

#contentForm {
  overflow: auto;
  height: 100%;
}

and moving to "skin.css"