Adds Cylinder helper class for cylinder info access in grantlee templates

to allow grantlee to access individual fields of the cylinder_t struct
rather than a string representation of the whole cylinder info using a
grantlee structure like this one:
	<table class="table_class">
		<tr>
			<td>Cylinder</td>
			<td>Start press.</td>
			<td>End press.</td>
			<td>Gas mix</td>
		</tr>
		{% for cylinderObject in dive.cylinderObjects %}
		<tr>
			<td>{{ cylinderObject.description }}</td>
			<td>{{ cylinderObject.startPressure }}</td>
			<td>{{ cylinderObject.endPressure }}</td>
			<td>{{ cylinderObject.gasMix }}</td>
		</tr>
		{% endfor %}
	</table>

Signed-off-by: Tim Wootton <tim@tee-jay.org.uk>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

core/subsurface-qt/CylinderObjectHelper.cpp

@@ -0,0 +1,37 @@
+#include "CylinderObjectHelper.h"
+#include "../helpers.h"
+
+static QString EMPTY_CYLINDER_STRING = QStringLiteral("");
+CylinderObjectHelper::CylinderObjectHelper(cylinder_t *cylinder) :
+	m_cyl(cylinder) {
+}
+
+CylinderObjectHelper::~CylinderObjectHelper() {
+}
+
+QString CylinderObjectHelper::description() const {
+	if (!m_cyl->type.description)
+		return QString(EMPTY_CYLINDER_STRING);
+	else
+		return QString(m_cyl->type.description);
+}
+
+QString CylinderObjectHelper::size() const {
+	return get_volume_string(m_cyl->type.size, true);
+}
+
+QString CylinderObjectHelper::workingPressure() const {
+	return get_pressure_string(m_cyl->type.workingpressure, true);
+}
+
+QString CylinderObjectHelper::startPressure() const {
+	return get_pressure_string(m_cyl->start, true);
+}
+
+QString CylinderObjectHelper::endPressure() const {
+	return get_pressure_string(m_cyl->end, true);
+}
+
+QString CylinderObjectHelper::gasMix() const {
+	return get_gas_string(m_cyl->gasmix);
+}