Use BeforePageDisplay hook to set the header ExportRDF <link>

I'd failed to understand why ExportRDF was set apart from
the header (using ParserTextProcessor), this is corrected now.

Lately someone juggled with the RL and unstyled content
have seem to appear therefore always load 'ext.smw.style'.

Change-Id: I5266b89c2880cfb261a0c50e596098c9714e0c6c
Merge "Use BeforePageDisplay hook to set the header ExportRDF <link>"