Added protocol option to Linker and OutputPage::addReturnTo.

Added protocol option to Linker and OutputPage::addReturnTo.

Added new argument to the Linker options array to allow
the forcing of an HTTP or HTTPS protocol. In order to facilitate
this, a protocol argument was added to Title::getLinkURL.

Also, an options argument was added to OutputPage::addReturnTo
so that options can be passed to the linker and so that the
returnto URL can be forced to a certain protocol.

Change-Id: Ia9cc11e310ad6ef23c221bdba3a4834e7c5556e7