[components] refactor main template header: make it much more flexible by using CtxComponent * rename userlink class (not private) with somewhat bw compat * make some cosmetic adjustements on log-in/registration components * update to component api, though this may breaks some sub-classes (for application customizing the breadcrumbs component for instance)

Latest changes 
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* table of `all latest changes`_

Links below is providing useful RQL query example.

.. _all latest changes: view?rql=Any+M%2CX+WHERE+X+modification_date+M+ORDERBY+M+DESC+LIMIT+30