Closes #20

An undocumented feature of uci:get_first() is to cast the returned value
to the same type as the default argument. Thus, supplying a default
value ot type number makes string.format superfluous.

This commit adds gluon-luci-core, a package both gluon-config-mode and
gluon-luci-admin will depend on. gluon-luci-core itself will depends on
gluon-luci-theme, gluon-core and most importantly luci-lib-web. It also
copies a few files from luci-mod-admin-core but leaves out everyting we
do not use.

At a later point I plan to move functionality from luci-lib-web into
this package, too. luci-lib-web contains most parts of luci including
hardcoded templates for CBI, which I intend to replace.

Otherwise the enable during image create will throw a few error messages

Display the correct hostname on the final page of configmode.
Previously, this page used to simply call luci.sys.hostname() which
would return the current hostname. However, when the configmode changes
the hostname luci.sys.hostname() will not reflect this. This patch
fetches the hostname directly from the UCI system config.

This adds a variable called 'hostname' which may be used in site.conf at
config_mode.msg_reboot and .msg_pubkey.

The reboot page should be delayed a little to give the browser time for
fetching assets (like the stylesheet). This adds a two second delay.
Unfortunately, I couldn't think of a sane way to do this within a luci
controller.

This patch forks the process. The parent will continue rendering the
page for the browser while the child will sleep and then reboot the
device. For this to work reliable the child needs to close stdout before
sleeping so the webserver closes the connection to the browser. This,
again, required a hack as lua does not allow closing std filehandles,
when prevented using luci.reboot() which was calling os.execute() and
that function will not work with stdout closed.

Those headings do not convey much information make the wizard less
compact. The help texts will be rewritten to guide the user instead.

Replace the inline stylesheet for the public key box on the reboot page
with a CSS class so it can be styled using the theme.

This makes gluon-config-mode and gluon-luci-admin depend on
gluon-luci-theme instead of luci-theme-openwrt.

The reset button resets the form. I don't think this is needed in a
wizard that simple and might confuse users so I removed it.

Due to my previous two commits configmode was broken when either meshvpn
or bandwidth limit was disabled. This fixes it but there may be a
cleaner solution provided by luci.

Hide the bandwidth limit checkbox when meshvpn is disabled.

Hide the downstream/upstream input fields when bandwitdh limiting is
disabled.

Now that haveged starts before the config mode, there is no need to explicity
depend on it; instead it is just used when specified in the site configuration.