Multi Select Dropdown / Auto-Reset

[lwe]

This PR adds the glue JavaScript code to automatically initialize any <select> using the materializecss .materialize_select() method. In addition it adds logic on top to correctly select / deselect items, for when a "reset" is required with in a situation like the following:

<select multiple data-mtl-select="multiple">
  <option value="">All items</option>
  <option value="1">First item</option>
  <option value="2">Second item</option>
</select>

So it properly selects / deselects the first element, but only when data-mtl-select="multiple" is used!

Demo

Syntax

<!-- Default dropdown -->
<select data-mtl-select>
  <option>First</option>
  <option>Second</option>
</select>

<!-- With "reset-to-first" feature -->
<select multiple data-mtl-select="multiple">
  <option value="">All</option> <!-- value MUST BE "" -->
  <option>First</option>
  <option>Second</option>
</select>

[lwe]

/cc @sled and @JorisM, might be useful for you too