MDL-59612 core: added previous and next links to activities

Part of MDL-59313.

course/templates/activity_navigation.mustache

@@ -0,0 +1,45 @@
+{{!
+    This file is part of Moodle - http://moodle.org/
+
+    Moodle is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Moodle is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
+{{!
+    @template core_course/activity_navigation
+
+    Displays the activity navigation
+
+    Context variables required for this template:
+    * prevlink - The link to the previous module the user can see
+    * nextlink - The link to the next module the user can see
+
+    Example context (json):
+    {
+        "prevlink": "<a href='#'>The origins of Moodle</a>",
+        "nextlink": "<a href='#'>Moodlers - are they contagious?</a>"
+    }
+}}
+<div>
+{{< core/columns-1to1to1}}
+    {{$column1}}
+        <div class="pull-left">
+            {{{prevlink}}}
+        </div>
+    {{/column1}}
+    {{$column3}}
+        <div class="pull-right">
+            {{{nextlink}}}
+        </div>
+    {{/column3}}
+{{/ core/columns-1to1to1}}
+</div>