Add project description field.

Description is shown in a popup when hovering the 'information' icon, like column description,
which is shown in project list on dashboard and in board's title.

This is useful to document the categories and colors used in the project.

app/Template/layout.php

@@ -35,7 +35,13 @@
     <?php else: ?>
         <header>
             <nav>
-                <h1><?= $this->a('K<span>B</span>', 'app', 'index', array(), false, 'logo', t('Dashboard')).' '.$this->summary($this->e($title)) ?></h1>
+                <h1><?= $this->a('K<span>B</span>', 'app', 'index', array(), false, 'logo', t('Dashboard')).' '.$this->summary($this->e($title)) ?>
+                    <?php if (! empty($description)): ?>
+                        <span class="column-tooltip" title="<?= $this->markdown($description) ?>">
+                            <i class="fa fa-info-circle"></i>
+                        </span>
+                    <?php endif ?>
+                </h1>
                 <ul>
                     <?php if (isset($board_selector) && ! empty($board_selector)): ?>
                     <li>