Use InputWidget facilities in byte limit counter

* Don't use setTimeout() within a change event, because change fires
  after the text has already changed
* Don't use .$input.val(), use .getValue() instead
* Don't use .placeholder()
** Reaching into .$input is bad
** Any use of .placeholder() is TextInputWidget's responsibility
** All browsers we support also support placeholder natively
* Remove .editSummaryByteLimit from ViewPageTarget, unused
* Remove ve.bind() wrapping, we already have var saveDialog = this;

Change-Id: I380575fec8d02d1191bfc1f3f235b94c64cd23b6
Merge "Use InputWidget facilities in byte limit counter"