Add Slack integration

app/Template/config/integrations.php

@@ -0,0 +1,22 @@
+<div class="page-header">
+    <h2><?= t('Integration with third-party services') ?></h2>
+</div>
+
+<form method="post" action="<?= $this->u('config', 'integrations') ?>" autocomplete="off">
+
+    <?= $this->formCsrf() ?>
+
+    <h3><i class="fa fa-slack fa-fw"></i>&nbsp;<?= t('Slack') ?></h3>
+    <div class="listing">
+        <?= $this->formCheckbox('integration_slack_webhook', t('Send notifications to a Slack channel'), 1, $values['integration_slack_webhook'] == 1) ?>
+
+        <?= $this->formLabel(t('Webhook URL'), 'integration_slack_webhook_url') ?>
+        <?= $this->formText('integration_slack_webhook_url', $values, $errors) ?>
+
+        <p class="form-help"><a href="http://kanboard.net/documentation/slack" target="_blank"><?= t('Help on Slack integration') ?></a></p>
+    </div>
+
+    <div class="form-actions">
+        <input type="submit" value="<?= t('Save') ?>" class="btn btn-blue"/>
+    </div>
+</form>