Signed-off-by: Jan-Tarek Butt <tarek@ring0.de>

* Use correct width
* Don't display focus outline (Webkit)
* Don't let option elements inherit error colors (Webkit)

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

This setting allows to enforce manually setting a hostname.

In the initial configuration, the hostname field is now left empty; when
setting the hostname is not enforced, the default hostname is shown as the
field placeholder.

Fixes #1139

Also add documentation about config mode settings.

Our VXLAN setup was changed to accept VXLAN packets without checksum almost
2 months ago, so we can disable sending the checksums now as well. Slightly
improves performance.

This package only provides the choice between "security" and "performance
mode". It should only be enabled when specified in site.mk.

The RFC standard multicast querier interval is 120s. Our querier uses in
interval of 20s for better support of roaming clients, but our robustness
setting of 3 leads to external queriers using the standard interval to be
timeout after only 60s, leading to frequent "querier appeared/disappeared"
messages. Increase robustness so that external queriers with any interval
<180s are supported.

Our provider modules are prefixed with gluon- now, and the log message
about a missing provider dir was confusing users.

We must ensure that each node becomes IGMP/MLD querier for its local
clients; having only a single querier for the whole mesh is generally
unreliable, leading to frequent "IGMP/MLD querier appeared/disappeared"
messages from batman-adv and unreliable snooping.

In smaller meshes it might be interesting only segment querier domains, but
allow membership reports to pass through the mesh, in order to support
snooping switches outside the mesh without special configuration. A
site.conf switch is provided to control this behaviour.

Fixes #1320

Fixes: 7ccdacd2 ("treewide: rework check_site_lib.lua")

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

- CGI script and index.html are moved from gluon-web to
  gluon-config-mode-core, the script is renamed to 'config'
- gluon-web and gluon-web-model base views and i18n files are symlinked
  into the new path
- gluon-web-theme is renamed to gluon-config-mode-theme and installs
  directly into the new path
- all gluon-web-* models, controllers and views are moved into the new
  path

Also bring back gluon-web-theme's i18n strings.

exec() is moved to gluon.util.