gluon-config-mode-*, gluon-web-admin: use new gluon.site library to avoid 'or {}' syntax

package/gluon-config-mode-contact-info/luasrc/lib/gluon/config-mode/wizard/0500-contact-info.lua

 return function(form, uci)
-	local site = require 'gluon.site_config'
+	local site = require 'gluon.site'
 
 	local owner = uci:get_first("gluon-node-info", "owner")
 
@@ -12,7 +12,7 @@ return function(form, uci)
 
 	local o = s:option(Value, "contact", translate("Contact info"), translate("e.g. E-mail or phone number"))
 	o.default = uci:get("gluon-node-info", owner, "contact")
-	o.optional = not ((site.config_mode or {}).owner or {}).obligatory
+	o.optional = not site.config_mode.owner.obligatory(false)
 	-- without a minimal length, an empty string will be accepted even with "optional = false"
 	o.datatype = "minlength(1)"
 	function o:write(data)

package/gluon-config-mode-geo-location/luasrc/lib/gluon/config-mode/wizard/0400-geo-location.lua

 return function(form, uci)
-	local site = require 'gluon.site_config'
+	local site = require 'gluon.site'
 
 	local location = uci:get_first("gluon-node-info", "location")
 
 	local function show_altitude()
-		if ((site.config_mode or {}).geo_location or {}).show_altitude ~= false then
+		if site.config_mode.geo_location.show_altitude(true) then
 			return true
 		end
 

package/gluon-web-admin/luasrc/lib/gluon/web/model/admin/remote.lua

@@ -13,7 +13,7 @@ You may obtain a copy of the License at
 local nixio = require "nixio"
 local fs = require "nixio.fs"
 local util = require "gluon.util"
-local site = require 'gluon.site_config'
+local site = require "gluon.site"
 
 local f_keys = Form(translate("SSH keys"), translate("You can provide your SSH keys here (one per line):"), 'keys')
 local s = f_keys:section(Section)
@@ -31,13 +31,13 @@ function keys:write(value)
 	end
 end
 
-local config = (site.config_mode or {}).remote_login or {}
-if not config.show_password_form then
+local config = site.config_mode.remote_login
+if not config.show_password_form(false) then
 	-- password login is disabled in site.conf
 	return f_keys
 end
 
-local min_password_length = config.min_password_length or 12
+local min_password_length = config.min_password_length(12)
 local mintype = 'minlength(' .. min_password_length .. ')'
 local length_hint