Revise all links to join to Curriki

We should go through all important places where registration or login is invited to and adjust the links the following manner:

• provided JavaScript is there, add an onclick handler so that it happens in the page
• change the href to /xwiki/bin/view/Registration/LoginOrRegister?xpage=popup

In code that makes the following:

<a onclick="Curriki.ui.login.displayLoginDialog('/xwiki/bin/view/Registration/LoginOrRegister?xpage=popup'); return false;" href="/xwiki/bin/view/Registration/LoginOrRegister?xpage=popup">

The header adds a bit in there so as to keep the current location.