Let gluon-respondd expose "MemAvailable" from /proc/meminfo to allow for
a more realistic memory-usage estimation.

Information on MemAvailable can be found here:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773

The field was accidentally removed during the status-page rewrite.

Fixes #1401

batman-adv-specific parts are moved to a new package
gluon-status-page-mesh-batman-adv.

gluon-status-page: reduce usage of absolute paths in cgi-bin scripts neighbours-nodeinfo and stations

The field is unused.

Some HTTP endpoints were writing annoying "broken pipe" messages to stderr.

A downside of this behaviour is that the page does not work for IPv4-only
clients, as the redirect will always point at an IPv6 address.

Still, it seems like a good idea to enforce the redirect even from the IPv4
next-node address, as switching nodes while being connected to the status
page would lead to unexpected behaviour.

All Access-Control-Allow-Origin are removed to improve users' privacy. As
the status page API is thus not useful without the status page anymore,
merge them back into a single package.

The status-page-api respondd provider is removed as well.

Fixes #1194

This new status page is significantly smaller than the old one. It always
loads its resources from the same host as the page itself, not requiring
cross-origin requests anymore.

It also uses the common i18n infrastructure of gluon-web.

Fixes #914

Add translation support to gluon-status-page, including English, German and Russian translations.

If cookies are disabled, the Statuspage only displays an empty ("Not connected")
This checks if the localStorage API is available and working and only uses it in this case
Also allows better backwards compatibility.

None of them are used by modern browsers anymore, so it's safe to remove them.

We have Git for history, there's no reason to keep old files that aren't
used anymore.

Fixes #698

It is not supported by all browsers yet.

Also change load display always to display 2 decimal digits (as it is read
from the kernel with 2 decimal digits).

Fixes #606

notUpdated is a Set, to a for-in loop doesn't work.

Fixes #657

Mobile browsers will often show or hide the address bar while scrolling.
This causes resize events which would often reset the signal graphs.

Fixes #662

Fixes #614

Allows simple handling of cached events.

On the status page statistics section counters for transmitted and received traffic were mixed up. Transmitted traffic was shown as received while received traffic was shown as being transmitted.

Fixes #586