Added loader for buttons

[Roene-JustBetter]

This will add a loader on a button when we are waiting for request for example inside the checkout. When you add loader on a button it will get a loader:

[royduin]

Why did you go for the loader icon instead of #922?

[Roene-JustBetter]

Checked this with @indykoning.

    {{ $attributes->merge([
        ':disabled' => $attributes->has('href') || $attributes->has(':href') || !$disableWhenLoading ? null : '$root.loading',
        'v-bind:class' => $loader ? '{ "button-loading": $root.loading }' : null
    ]) }}

Is not working.

[indykoning]

In more details the blade compiler seems to fail due to the { within the {{ ...->merge creating a corrupted php file akin to

    {{ $attributes->merge([
        ':disabled' => $attributes->has('href') || $attributes->has(':href') || !$disableWhenLoading ? null : '$root.loading',
        'v-bind:class' => $loader ? ') 'button-loading' => false
     }}

[royduin]

Please sync with master and double check the screenshot changes.