gluon-web-model: Add support for "Supramaps"

It was not possible to modularize single sections of forms in the config mode.
This commit adds support for ´Supramaps´. Using supramaps it is possible to create an additional directory where inframaps reside.
E.g. a Lua model file with a same-named directory (excluding the file extension) defines a Form element and returns it. This is a supramap.
If Lua files exist in that directoryn the Form element is available in their environment as "Supramap".
Thus these files can add additional sections which are "inframaps" and must return the modified supramap.
This allows e.g. modularizing the password field in the gluon-web-admin package as an own package without hampering usability.

package/gluon-web-model/luasrc/usr/lib/lua/gluon/web/model.lua

@@ -4,6 +4,7 @@
 
 module('gluon.web.model', package.seeall)
 
+local glob = require 'posix.glob'
 local unistd = require 'posix.unistd'
 local classes = require 'gluon.web.model.classes'
 
@@ -11,12 +12,13 @@ local util = require 'gluon.web.util'
 local instanceof = util.instanceof
 
 -- Loads a model from given file, creating an environment and returns it
-local function load(filename, i18n)
+local function load(filename, i18n, supra)
+	supra = supra or {}
 	local func = assert(loadfile(filename))
 
 	setfenv(func, setmetatable({}, {__index =
 		function(tbl, key)
-			return classes[key] or i18n[key] or _G[key]
+			return supra[key] or classes[key] or i18n[key] or _G[key]
 		end
 	}))
 
@@ -37,6 +39,8 @@ return function(config, http, renderer, name, pkg)
 
 	local modeldir = config.base_path .. '/model/'
 	local filename = modeldir .. name .. '.lua'
+	local infradir = modeldir .. name .. '/'
+	local infrafnames = glob.glob(infradir .. '*.lua') or {}
 
 	if not unistd.access(filename) then
 		error("Model '" .. name .. "' not found!")
@@ -50,6 +54,19 @@ return function(config, http, renderer, name, pkg)
 
 	local maps = load(filename, i18n)
 
+	if #infrafnames > 0 and #maps ~= 1 then
+		error("'" .. name .. "' has got inframaps. It must return a single supramap!")
+	end
+
+	for _, f in ipairs(infrafnames) do
+		local m = load(f, i18n, { Supramap = maps[1] })
+		if #m ~= 1 then
+			error("Inframodule '" .. f:sub(#modeldir) .. "' must return the inherited supramap!")
+		end
+		hidenav = hidenav or maps[1].hidenav or m[1].hidenav
+		maps[1] = m[1]
+	end
+
 	for _, map in ipairs(maps) do
 		map:parse(http)
 	end