mvc/view: Create layout_partials/base_apply_button to centralize design of the standard Apply button

[Monviech]

Fixes: #8284

Example of generated HTML with the KEA example implementation:

<section class="page-content-main">
    <div class="content-box">
        <div class="col-md-12">
            <br>
            <div id="change_message_base_form" class="alert alert-info" style="display: none;" role="alert">
                After changing settings, please remember to apply them.            </div>
            <button class="btn btn-primary" id="reconfigureAct" data-endpoint="/api/kea/service/reconfigure" data-label="Apply" data-error-title="Error reconfiguring service." type="button"><b>Apply</b> <i class="reload_progress"></i></button>
            <br><br>
        </div>
    </div>
</section>

[AdSchellevis]

I think this will further simplify our templates, which is good, but I do have some concerns which I've added in the comments.

[Monviech]

Merged as discussed with @AdSchellevis