Temporarily disable global feed updates

Due to a high resource consumption the global updater now is
unavailable. Later it will be replaced by an AJAX query.
Fix unread counter

Another variable was necessary as before.
Make Feed Library two-columned

For better experience on bigger screens the Feed Library now shows up
two feeds together in one 'row'.

As before, on displays with less than 600px screen width (mobile
devices especially) the feeds will be shown one per row.
Fix XML locator for urls without 'http'

Sometimes the RSS feed locator returned URLs without the 'http://'
prefix causing an issue where regarding XMLs weren’t found.
Attempt to fix updater problem

Not completed yet. We have to move to AJAX to make the process more
user and server-friendly.