#640: Support SJS with a language property

[prestonmcgowan]

Add sjs to your request
definition to make use of a SJS controller.
More comments added to Issue #640.

[dmcassel]

This requires adding the parameter on every call -- feels error prone. I like including this, but also controlling the default (xquery vs sjs). To do that, we would:

1. add a "controller-ext" property to default.properties, with a default value of "xqy"
2. add declare variable $c:CTRL-EXT := ("@ml.controller-ext", $def:CTRL-EXT)[1]; to src/app/config/config.xqy
3. add declare variable $CTRL-EXT := "xqy"; to src/roxy/config/defaults.xqy
4. in src/roxy/router.xqy: `declare variable $language as xs:string := req:get("language", $config:CTRL-EXT, "type=xs:string");

I'd have to test to make sure that's right, but I think that will do it. Then you could add

controller-ext=sjs

to your build.properties and default to SJS controllers, but still override if needed. Want me to send that change to your PR, or would you like to make that update?

[prestonmcgowan]

Changes made and committed.
Updated sample code on #640.
Please review.

[dmcassel]

Looks great. Thanks for the PR!