gluon-luci-admin: disable when not in configmode

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.
gluon-luci-admin: fix indentation

Replaces double-spaces with tabs to match surrounding code.
gluon-luci-admin: no logout button in configmode

Hide the "logout" button when in configmode.
gluon-luci-admin: remove redundant headings
gluon-luci-admin: replace overview text

This completely replaces the text on the overview page. Consider this a
placeholder until someone writes a better suited version :)
gluon-luci-admin: reboot.html, remove refresh

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.