Misc: Get rid of the legacy defaults.lua globals (#9546)

* This removes support for the following deprecated constants: `DTAP_ZONE_FLIPPING`, `DTAP_ZONE_BOOKMARK`, `DCREREADER_CONFIG_DEFAULT_FONT_GAMMA`
* The "Advanced settings" panel now highlights modified values in bold (think about:config in Firefox ;)).
* LuaData: Isolate global table lookup shenanigans, and fix a few issues in unused-in-prod codepaths.
* CodeStyle: Require module locals for Lua/C modules, too.
* ScreenSaver: Actually garbage collect our widget on close (ScreenSaver itself is not an instantiated object).
* DateTimeWidget: Code cleanups to ensure child widgets can be GC'ed.

reader.lua

@@ -21,18 +21,16 @@ local userpatch = require("userpatch")
 userpatch.applyPatches(userpatch.early_once)
 userpatch.applyPatches(userpatch.early)
 
--- Load default settings
-require("defaults")
-local DataStorage = require("datastorage")
-pcall(dofile, DataStorage:getDataDir() .. "/defaults.persistent.lua")
-
-
 io.stdout:write(" [*] Version: ", require("version"):getCurrentRevision(), "\n\n")
 io.stdout:flush()
 
+-- Load default settings
+G_defaults = require("luadefaults"):open()
+
 -- Read settings and check for language override
 -- Has to be done before requiring other files because
 -- they might call gettext on load
+local DataStorage = require("datastorage")
 G_reader_settings = require("luasettings"):open(
     DataStorage:getDataDir().."/settings.reader.lua")