Clarify our OOP semantics across the codebase (#9586)

Basically:

* Use `extend` for class definitions
* Use `new` for object instantiations

That includes some minor code cleanups along the way:

* Updated `Widget`'s docs to make the semantics clearer.
* Removed `should_restrict_JIT` (it's been dead code since https://github.com/koreader/android-luajit-launcher/pull/283)
* Minor refactoring of LuaSettings/LuaData/LuaDefaults/DocSettings to behave (mostly, they are instantiated via `open` instead of `new`) like everything else and handle inheritance properly (i.e., DocSettings is now a proper LuaSettings subclass).
* Default to `WidgetContainer` instead of `InputContainer` for stuff that doesn't actually setup key/gesture events.
* Ditto for explicit `*Listener` only classes, make sure they're based on `EventListener` instead of something uselessly fancier.
* Unless absolutely necessary, do not store references in class objects, ever; only values. Instead, always store references in instances, to avoid both sneaky inheritance issues, and sneaky GC pinning of stale references.
  * ReaderUI: Fix one such issue with its `active_widgets` array, with critical implications, as it essentially pinned *all* of ReaderUI's modules, including their reference to the `Document` instance (i.e., that was a big-ass leak).
* Terminal: Make sure the shell is killed on plugin teardown.
* InputText: Fix Home/End/Del physical keys to behave sensibly.
* InputContainer/WidgetContainer: If necessary, compute self.dimen at paintTo time (previously, only InputContainers did, which might have had something to do with random widgets unconcerned about input using it as a baseclass instead of WidgetContainer...).
* OverlapGroup: Compute self.dimen at *init* time, because for some reason it needs to do that, but do it directly in OverlapGroup instead of going through a weird WidgetContainer method that it was the sole user of.
* ReaderCropping: Under no circumstances should a Document instance member (here, self.bbox) risk being `nil`ed!
* Kobo: Minor code cleanups.

frontend/apps/reader/modules/readerdictionary.lua

@@ -6,7 +6,6 @@ local DictQuickLookup = require("ui/widget/dictquicklookup")
 local Event = require("ui/event")
 local Geom = require("ui/geometry")
 local InfoMessage = require("ui/widget/infomessage")
-local InputContainer = require("ui/widget/container/inputcontainer")
 local InputDialog = require("ui/widget/inputdialog")
 local JSON = require("json")
 local KeyValuePage = require("ui/widget/keyvaluepage")
@@ -16,6 +15,7 @@ local NetworkMgr = require("ui/network/manager")
 local SortWidget = require("ui/widget/sortwidget")
 local Trapper = require("ui/trapper")
 local UIManager = require("ui/uimanager")
+local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local ffi = require("ffi")
 local C = ffi.C
 local ffiUtil  = require("ffi/util")
@@ -60,9 +60,9 @@ local function getIfosInDir(path)
     return ifos
 end
 
-local ReaderDictionary = InputContainer:new{
+local ReaderDictionary = WidgetContainer:extend{
     data_dir = nil,
-    dict_window_list = {},
+    dict_window_list = nil, -- array
     lookup_msg = _("Searching dictionary for:\n%1"),
 }
 
@@ -100,6 +100,7 @@ local function getDictionaryFixHtmlFunc(path)
 end
 
 function ReaderDictionary:init()
+    self.dict_window_list = {}
     self.disable_lookup_history = G_reader_settings:isTrue("disable_lookup_history")
     self.dicts_order = G_reader_settings:readSetting("dicts_order", {})
     self.dicts_disabled = G_reader_settings:readSetting("dicts_disabled", {})
@@ -156,7 +157,7 @@ function ReaderDictionary:init()
     self:updateSdcvDictNamesOptions()
 
     if not lookup_history then
-        lookup_history = LuaData:open(DataStorage:getSettingsDir() .. "/lookup_history.lua", { name = "LookupHistory" })
+        lookup_history = LuaData:open(DataStorage:getSettingsDir() .. "/lookup_history.lua", "LookupHistory")
     end
 end