Input: Process input events in batches (#7483)

Requires https://github.com/koreader/koreader-base/pull/1344 & https://github.com/koreader/koreader-base/pull/1346 (fix #7485)

Assorted input fixes:

* Actually handle errors in the "there's a callback timer" input polling loop.
* Don't break timerfd when the clock probe was inconclusive.

Not directly related, but noticed because of duplicate onInputEvent handlers:

* HookContainer: Fix deregistration to actually deregister properly. "Regression" extant since its inception in #2933 (!).
* Made sure the three plugins (basically the trio of AutoThingies ;p) that were using HookContainer actually unschedule their task on teardown.

spec/unit/device_spec.lua

@@ -274,13 +274,15 @@ describe("device module", function()
             mock_ffi_input = require('ffi/input')
             stub(mock_ffi_input, "waitForEvent")
             mock_ffi_input.waitForEvent.returns(true, {
-                type = 3,
-                time = {
-                    usec = 450565,
-                    sec = 1471081881
-                },
-                code = 24,
-                value = 16
+                {
+                    type = 3,
+                    time = {
+                        usec = 450565,
+                        sec = 1471081881
+                    },
+                    code = 24,
+                    value = 16
+                }
             })
 
             local UIManager = require("ui/uimanager")