Data binding and style fixes

* added portfolio, mentors and management YAML files to be used in templating
* fixed issue with landing page not working properly in mobile view
* removed annoying page style that was applied to everything
* improved text sizes in various views
* reworked mentors view styles
* rearranged landing page vector graphics to match their meaning more
* code style improvements

_includes/header.html

@@ -1,7 +1,7 @@
 <!-- header.scss -->
 <nav class="navigation">
   <a href="/" {% if page.url == '/' %}style="display: none;"{% endif %}>
-	<img class="logo" src="{{ "/assets/logo.svg " | relative_url }}">
+	<img id="header-logo" class="logo" src="{{ "/assets/logo.svg " | relative_url }}">
   </a>
 
   <div class="menu">

_includes/main_nav.html

@@ -1,4 +1,5 @@
 <li><a href="/student">Tudengile</a></li>
+<li><a href="/mentors">Mentorid</a></li>
 <li><a href="/helpdesk">Helpdesk</a></li>
 <li><a href="/ourwork">Ettevõttele</a></li>
 <li><a href="/aboutus">Lapikutest</a></li>