Added module header feature to SCL language.

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