Fixes https://github.com/codemirror/CodeMirror/issues/3215

When closeOnEnter is disabled the enter event never gets default
prevented this causes issues for IE9/10, this way implementors can
optionally preventDefault if they want

Closes #2866

Issue #2777

* closeOnEnter: whether or not the dialog should be closed when you
  press enter with it focused. Defaults to true.

* closeOnBlur: whether or not the dialog should be closed when the
  textfield or button loses focus. Defaults to true.

* onClose: a callback that will be called when the close function
  completes.

* onInput: very similar to onKeyDown, but uses the input event instead
  of keydown. Just an additional event handler basically.

Bumping them for every release just adds too much git
noise and history blowup.

Issue #2191

Remove callback argument, save currently open dialog in per-editor state.

Closes #1133