All functionality that is common between components should be in this folder.
A mixin object:

```js
export default {
  props: {
    ...
  },
  data: function() {
    ...
  },
  methods: {
    ...
  },
};
```

can be merged into component like this:

import ExampleMixin from '@/mixins/ExampleMixin';
// then, add to options:
mixins: [ExampleMixin],

See https://vuejs.org/v2/guide/mixins.html.
