UI Behavior tweaks (#3983)

* Switch all initial highlights to "fast" update

i.e., everything that does an invert
Plus a few other things that refresh small UI elements onTap
Re #3130

* Tweak refreshtype for a number of widgets:
  * Fix iconbutton dimen
  * Make touchmenu flash on close & initial menu popup. Full-screen on close.
  * Use flashing updates when opening/closing dictionary popup. Full-screen on close.
  * Switch FileManager to partial.
    It's mostly text, and we want flash promotion there.
  * Make configdialog & menu flash on exit
  * Make FLWidget flash on close
  * virtualkeyboard: flash on layout change & popup.
  * Potentially not that great workaround to ensure we actually see the
highlights in the FM's chevrons
  * Flash when closing BookStatus Widget
  * Optimize away a quirk of the dual "fast" update in touchmenu

* Promote updates to flashing slightly more agressively.

* Document what each refreshtype actually does.

With a few guidelines on their optimal usecases.

* Switch remaining scheduleIn(0.0) to nextTick()

* Tighter scheduling timers

Shaving a hundred ms off UI callbacks...

* Cache FFI C Library namespace

* Ask MuPDF to convert pixmaps to BGR on Kobo

Fix #3949

* Mention koxtoolchain in the README

re #3972

* Kindle: Handle *all* fonts via EXT_FONT_DIR instead of bind mounts insanity

* Make black flashes in UI elements user-configurable

(All or nothing).

* Jot down some random KOA2 sysfs path

frontend/ui/message/streammessagequeue.lua

@@ -5,6 +5,7 @@ local MessageQueue = require("ui/message/messagequeue")
 local _ = require("ffi/zeromq_h")
 local zmq = ffi.load("libs/libzmq.so.4")
 local czmq = ffi.load("libs/libczmq.so.1")
+local C = ffi.C
 
 local StreamMessageQueue = MessageQueue:new{
     host = nil,
@@ -13,7 +14,7 @@ local StreamMessageQueue = MessageQueue:new{
 
 function StreamMessageQueue:start()
     self.context = czmq.zctx_new();
-    self.socket = czmq.zsocket_new(self.context, ffi.C.ZMQ_STREAM)
+    self.socket = czmq.zsocket_new(self.context, C.ZMQ_STREAM)
     self.poller = czmq.zpoller_new(self.socket, nil)
     local endpoint = string.format("tcp://%s:%d", self.host, self.port)
     logger.warn("connect to endpoint", endpoint)
@@ -24,7 +25,7 @@ function StreamMessageQueue:start()
     local id_size = ffi.new("size_t[1]", 256)
     local buffer = ffi.new("uint8_t[?]", id_size[0])
     -- @todo: check return of zmq_getsockopt
-    zmq.zmq_getsockopt(self.socket, ffi.C.ZMQ_IDENTITY, buffer, id_size)
+    zmq.zmq_getsockopt(self.socket, C.ZMQ_IDENTITY, buffer, id_size)
     self.id = ffi.string(buffer, id_size[0])
     logger.dbg("id", #self.id, self.id)
 end