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.
Allows the device to go into standby (if available in `/sys/power/state`) to save power.
Adds an entry in the device menu to tune the timeout for standby.
(Shows total standby- and suspend-time in system statistics.)
FocusManager: fix round x use y layout
FocusManager: add tab and shift tab focus navigation support
FocusManager: handle Press key by default
FocusManager: make sure selected in instance level
FocusManager: add hold event support
FocusManager: Half move instead of edge move
FocusManager: add keymap override support
FocusManager: refocusWidget will delegate to parent FocusManager
Focusmanager: refocusWidget can execute on next tick
inputtext: can move out of focus on back
inputtext: fix cannot exit for non-touch device
inputtext: fix cannot input text with kindle dx physical keyboard
fontlightwidget: add non-touch support
datetimewidget: add non-touch support
datetimewidget: fix set date failed in kindle DX, fix datetimewidget month range to 1~23 by default
datetimewidget: make hour max value to 23
multiinputdialog: add non-touch support
checkbox: focusable and focus style
virtualkeyboard: no need to press two back to unfocus inputtext
virtualkeyboard: collect FocusManager event key names to let VirtualKeyboard disable them
openwithdialog: add non-touch support
inputdialog: can close via back button
enable all InputDialog and MultiInputDialog can be close by back
keyboardlayoutdialog: non-touch support
readertoc: non touch device can expand/collapse in toc
bookstatuswidget: non touch support
keyvaluepage: non-touch support
calendarview: non-touch support
Move Default and extra buttons above Cancel/OK.
Default values shown in the default button.
Precisions can be set for both values separately.
Minor geometry fix for consistence with SpinWidget.
