Introduce multi-select module picker

Introduce a multi-select module dropdown, to replace the module selector.

Features

This replaces the module select dropdown with a dropdown that opens up into a multi-selector.

• Multi-select window with checkboxes and scrolling.
• Search box for filtering by module or test name.
• "Apply" button to run selected tests or modules.
• "Reset" button to clear selection, returning to implied default of "Select all".

Accessibility

• Display current module section (comma-separated) in placeholder and tooltip text.
• Close on Escape keydown.

<figure> <figcaption markdown="span">[QUnit 1.23.1 demo](https://codepen.io/Krinkle/full/QwLZWWe)</figcaption> </figure> <figure> <figcaption markdown="span">[QUnit 2.0.0 demo](https://codepen.io/Krinkle/full/mybzddj)</figcaption> </figure>

See also

• Update UI to allow multiple test/module selection · Issue #953
• HTML Reporter: Add multi-select module dropdown · Pull Request #973
• HTML Reporter: Improve toolbar styles & accessibility · Pull Request #989
• [QUnit 2.0.0 Release]({% post_url 2016-06-16-qunit-2-0-0 %})