Change Start page to no longer dial home by default.

When starting FreeCAD for the first time, it load the HTML content of
src/Mod/Start/StartPage/StartPage.html and show it as a friendly startup page.
Unfortunately, one of the tabs in the startup page is an iframe loading the content of
https://blog.freecadorg/.  The effect is that every time one start FreeCAD, it dial
home over the Internet with a HTTP request to the mentioned URL.  This is a privacy
problem.  At the moment the blog page in turn will connect to https//i0.wp.com/ and
https//s0.wp.com/, in effect also reporting the startup to Wordpress.  Please do not
dial out without the expressed approval and on request of the user of the program.

This patch change the startup page to instead of putting the blog posts in a tab, it
will link to the blog and the connection is only established when the user click on
'BLOG' in the start page.  It include a link tooltop to make it easier to understand
that this will bring the user to a new page.

src/Mod/Start/StartPage/StartPage.html

@@ -21,7 +21,8 @@
                 <li><a id="htab1" class="active" onClick="toggle('tab1')" href="#">T_DOCUMENTS</a></li>
                 <li><a id="htab2" onClick="toggle('tab2')" href="#">T_HELP</a></li>
                 <li><a id="htab3" onClick="toggle('tab3')" href="#">T_ACTIVITY</a></li>
-                <li><a id="htab4" onClick="toggle('tab4')" href="#">BLOG</a></li>
+                <li><a href="https://blog.freecad.org/" title="Link to the
+FreeCAD blog">BLOG</a></li>
             </ul>
             <div id="tab1" class="panel">
                 
@@ -157,11 +158,6 @@
                 </div>
 
             </div>
-
-            <div id="tab4" class="panel hidden iframecontainer">
-                <iframe src="https://blog.freecad.org/" title="Freecad Blog" class="iframe" ></iframe> 
-            </div>
-
         </div>
     </body>
 </html>