Such Great Heights Beta 1 (v3.0.0-beta.1)

• [BREAKING] Update addon repo to ember 3.5, drop support for Ember 2.4 #265 (lukemelia)
• use closure actions #264 (mcfiredrill)
• Handle when App.rootElement can be a node, rather than an id #263 (averydev)
• update README.md Custom Modals section #259 (hakilebara)
• Update .travis.yml #258 (samselikoff)
• Don't sendAction in click handler when component isDestroying or isDestroyed #255 (oscarni)

This release will become v3.0.0 final if no issues are found in the next 2 days.