closes https://github.com/TryGhost/Ghost/issues/8463
- move generic text input handling into `text-input` mixin so it applies to text inputs and textareas
- adds `autoExpand` property to `gh-textarea` that accepts a selector to watch for resize changes, if the property is set then auto-expanding behaviour is triggered any time the textarea value is changed or when the selector element is resized (this prevents change in textarea width from toggling nav or split screen mode resulting in textarea content being hidden or the textarea being taller than it's contents)
- adds `ember-element-resize-detector` addon to allow watching of element resizes rather than window resizes (this was already included as a sub-dependency via `ember-light-table`->`ember-scrollable`->`ember-element-resize-detector`)
no issue
- add ember-suave dependency
- upgrade grunt-jscs dependency
- add a new .jscsrc for the client's tests directory that extends from client's base .jscsrc
- separate client tests in Gruntfile jscs task so they pick up the test's .jscsrc
- standardize es6 usage across client
