Added module header feature to SCL language.

Module header must be in the beginning of the module. However, comments
are allowed before the header. Header has the following form:
    module {
        field = value,
        field = value
    }

Currently field name classLoader is supported. It makes it possible to
specify which classLoader is used to resolve importJava declarations.
    module {
        classLoader = "my.bundle.name.somewhere"
    }

refs #6931

Change-Id: Ibca2152597a738d1e4641cf6262af06069b38af5