ace-window.el (aw--doit): use map with most priority

* ace-window.el (aw--doit): Use `set-transient-map' instead of `(setq
  overriding-local-map)`, as it has more priority and `helm' is using
  it. This will avoid the current conflict with helm.

Re #15.
ace-window.el (aw--doit): fix conflict with helm

* ace-window.el (aw--doit): Need to remove `helm--maybe-update-keymap'
  from `post-command-hook'. Otherwise, even if not in the helm
  minibuffer, the helm transient map will override all bindings.

Fixes #15.