[Experiment] autoDisableInputMethodWhenLeavingInsertMode

This is retry of #151. Why? I found @frapples's vim-mode-plus-patch-switch-ime. It use readOnly attribute instead of setting input.type to password as in #151. And as far as I checked, no Cannot move tab when it is in normal mode #193 issue as like it was in #151.

This time, I made this as opt-in configuration. To use this feature, need to enable autoDisableInputMethodWhenLeavingInsertMode.

Ideally implement old feature request(atom/atom#1092) in atom-core is the best.
- But it's not likely to happen soon.
Once I merged PR #151, it seemed to work as we want.
But I removed(#205) when I noticed Cannot move tab when it is in normal mode #193.
After a while some plugin packages were released to tackle this issue
- vim-mode-plus-auto-ime invoke external command to manipulate IME.
- vim-mode-plus-patch-switch-ime is like #151, but use readOnly attribute instead of set input's type t password.

t9md / atom-vim-mode-plus