gluon-luci-admin: various changes

add new luci-theme

Don't refresh the reboot page after rebooting the node. It's not going
back to configmode anyway so it'll never reload without user
intervention.

This completely replaces the text on the overview page. Consider this a
placeholder until someone writes a better suited version :)

Hide the "logout" button when in configmode.

Replaces double-spaces with tabs to match surrounding code.

For security reasons we'd like to disable all HTTP config interfaces
when the node is operating normally. This patch disables gluon-luci-admin
when configmode is not enabled.

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.

This is the initial version of our new configmode theme. It's far from
finished but at least configmode looks good. There are lots of
declarations copied from OpenWRT's default theme so most other luci
modules would be somewhat usable when shown using this theme.

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.

This way we have a kind of load balancing among the mirrors.

This adds a list of known models to the readme.

Instead of a single url this patch allows to have a list of urls. So in case
of network instability a router can still reach local mesh-cloud server to pull
a update from. In this stage the autoupdater simply tries every mirror until
one passes all tests.

This also removes the need for the cleanup function. Instead the cleanup
code is moved in place.

Move building blocks of the update into seperate functions.