InputContainer: Fall cleanup ;).

Get rid of the doc & seqtext fields, as they are not actually used (nor
are they particularly useful, the event handler's name should be pretty
self-explanatory).

Also, tweak the key_events documentation to highlight the quirks of the
API, especially as far as array nesting is involved...

Random drive-by cleanup of the declarations of key_events & ges_events
to re-use the existing instance object (now that we know they're sane
;p) for tables with a single member (less GC pressure).

frontend/ui/widget/scrollhtmlwidget.lua

@@ -79,8 +79,8 @@ function ScrollHtmlWidget:init()
 
     if Device:hasKeys() then
         self.key_events = {
-            ScrollDown = {{Input.group.PgFwd}, doc = "scroll down"},
-            ScrollUp = {{Input.group.PgBack}, doc = "scroll up"},
+            ScrollDown = { { Input.group.PgFwd } },
+            ScrollUp = { { Input.group.PgBack } },
         }
     end
 end