Hazard Curves in multiple imts

[matley]

Hazard Curves in multiple IMTs needs to be exported mainly for the sake of consistency as the change due to https://bugs.launchpad.net/openquake/+bug/1160427

A suggested implementation is exemplified as follows.

(The intent is to reuse the current schema for hazard curves and to not break any script that parses exported curves in a single imt)

<?xml version="1.0" encoding="utf-8"?>
<nrml xmlns:gml="http://www.opengis.net/gml"
      xmlns="http://openquake.org/xmlns/nrml/0.4">

    <!-- Spectral Acceleration (SA) example -->
    <hazardCurves sourceModelTreePath="b1_b2_b4" gsimTreePath="b1_b2" investigationTime="50.0" IMT="SA" saPeriod="0.025" saDamping="5.0">
        <IMLs>5.0000e-03 7.0000e-03 1.3700e-02</IMLs>

        <hazardCurve>
            <gml:Point>
                <gml:pos>-122.5000 37.5000</gml:pos>
            </gml:Point>
            <poEs>9.8728e-01 9.8266e-01 9.4957e-01</poEs>
        </hazardCurve>
        <hazardCurve>
            <gml:Point>
                <gml:pos>-123.5000 37.5000</gml:pos>
            </gml:Point>
            <poEs>9.8728e-02 9.8266e-02 9.4957e-02</poEs>
        </hazardCurve>
    </hazardCurves>

    <!-- Basic example, using PGA as IMT -->
    <hazardCurves sourceModelTreePath="b1_b2_b3" gsimTreePath="b1_b7" investigationTime="50.0" IMT="PGA">
        <IMLs>5.0000e-03 7.0000e-03 1.3700e-02</IMLs>

        <hazardCurve>
            <gml:Point>
                <gml:pos>-122.5000 37.5000</gml:pos>
            </gml:Point>
            <poEs>9.8728e-01 9.8266e-01 9.4957e-01</poEs>
        </hazardCurve>
        <hazardCurve>
            <gml:Point>
                <gml:pos>-123.5000 37.5000</gml:pos>
            </gml:Point>
            <poEs>9.8728e-02 9.8266e-02 9.4957e-02</poEs>
        </hazardCurve>
    </hazardCurves>
</nrml>

[matley (matley)]

https://github.com/gem/oq-nrmllib/pull/86