gluon-cron: Fix endless loop parsing invalid lines

Using the line
```
* * * * echo "foobar"
```
(notice the missing fifth time field) in a crontab causes gluon-cron
to enter an endless loop while parsing it, thus it won't even execute
the other, valid crontabs.

This is caused by the loop in [line 138] where `begin - min`
substracts the unsigned `min` from the signed `begin`. If now `begin`
is invalid, `strict_atoi` returns -1 and the loop starts at
`(-1)-1=MAX_INT` and runs while `i <= MAX_INT` which is always true.

The real culprit lies in [line 134] where exactly this case
`begin < min` is checked - but because of the signedness, this check doesn't
work as expected either.

The easiest solution is to make `min` a signed integer instead of an unsigned
one, as we do not require it to be very large and only pass the constants 0 or
1 to it.

To avoid other similar problems, this patch makes the input variable `n` a
signed integer as well.

mesh-batman-adv-core: add clientcount statistics

in case a target does not use overlayfs

Since switching to Barrier Breaker/procd, we'd not notice if we were
upgrading from a version before renaming the config file to gluon-setup-mode
as the upgrade scripts run after the preinit.

Fix this by checking later during setup mode init again and rebooting into the
regular run mode if we detect this case.

Die Bezeichnung "Mesh-VPN" ist etwas irreführend. Man kann denken, dass hiermit das Meshing aktiviert wird, wobei es ja — im Gegenteil — um eine Nutzung des WAN geht.

This adds

  "client" { "total": <int>, "wifi": <int>" }

to statistics.d. "total" will be the number of clients connected.
"wifi" will be the number of clients connected over wifi. I.e. "total"
will always be equal to or greater than "wifi".

The node will not count itself.

Configurable WAN

luci-theme: fix centering of form fields

gluon-announced: fix help message

It incorrectly stated "-m" to be the multicast group option, when it really was "-g"

This reverts commit f37f1f1ac2c9a44d0aafb25e3f5a01e16df6019e.

previously it was gluon-luci-privatewifi

The package luci-base now contains everything we need.

To start after haveged after the recent update.

gluon-luci-private-wifi: UI for enabling a private WLAN

This commit splits gluon-config-mode into several, mostly independent
packages.

* gluon-config-mode-core: basic functionality (required)
* gluon-config-mode-hostname: hostname field
* gluon-config-mode-autoupdater: show when autoupdater is enabled
* gluon-config-mode-mesh-vpn: fastd vpn configuration, bw limit
* gluon-config-mode-geo-location: geo coordinates
* gluon-config-mode-contact-info: contact info field

The package gluon-config-mode has been removed. You need to replace
it with these packages (or any subset of them) in site.mk:

* gluon-config-mode-hostname
* gluon-config-mode-autoupdater
* gluon-config-mode-mesh-vpn
* gluon-config-mode-geo-location
* gluon-config-mode-contact-info

Note: It is not possible to deactivate the autoupdater in config mode
anymore (expert mode will still allow it). Instead, a message is shown
in case the autoupdater is enabled.

freifunk-gluon/gluon#122

The specification says that the ifa_addr field of struct ifaddrs may be NULL,
and in Barrier Breaker, this does actually occur...

Make it clear that saving settings will reboot the device.

config-mode, mesh-vpn: refactor key generation