[Bugfix] Select - simple array case

[mike-north]

Fixes #74

This introduces test coverage for simple array use cases in select, switches, checks and radios.

Example:

Component

export default Ember.Component.extend({
  choices: ['Dexter Morgan', 'Deborah Morgan', 'Harry Morgan'],
  selectedChoice: 'Deborah Morgan'
});

Template

{{md-select
  content=choices
  value=selectedChoice}}

or

{{md-radios
  content=choices
  selection=selectedChoice}}