more customization for @cookieconsentbutton

[raymanP]

• added btnattributes for @cookieconsentbutton to allow button customizing
• removed button label escaping to allow html labels

Example:

@cookieconsentbutton(action: 'reset', label: '<i class="material-icons" style="font-size: 2em">shield</i>',
  attributes: ['id' => 'reset-button', 'class' => 'btn fixed-bottom cookie-reset'],
  btnattributes: ['class' => 'btn bg-transparent', 'style' => 'margin-left: 5px; margin-bottom:5px',
    'data-toggle' => 'tooltip', 'title' => __('cookieConsent::cookies.manage')])

Covers #43