Salmon crumble

This version includes new features and some significant changes

• [BREAKING] Update to ember-basic-dropdown 0.7.0-beta.1. This means that the component is opened/
  closed using mousedown instead of click. This makes the component feel more snappy. It is unlikeliy
  that this breaks real world usage but might break integration tests of people where people rely
  on $('.ember-power-select-trigger').click().
• [FEATURE] New action: onfocus. Unsurprisingly it is invoked when the component gains focus.
  It receives (dropdown, event) and can be used, by example, to open the component on focus.
• [FEATURE] EPS now accepts a opened boolean property used to open/close the component
  without triggering events on it. Useful to render the component already opened.