[TASK] Add all_fields marker explanation

Resources/Private/Language/de.locallang.xlf

@@ -260,6 +260,10 @@ Bitte registrieren Sie Ihre Templates in den entsprechenden ext_localconf.php Da
 				<source><![CDATA[Marker]]></source>
 				<target><![CDATA[Marker]]></target>
 			</trans-unit>
+			<trans-unit id="backend.marker.allFields" approved="yes">
+				<source><![CDATA[A table of all available given markers and corresponding values. Some variables can't be shown correctly like objects.]]></source>
+				<target><![CDATA[Eine Tabelle mit allen verfügbaren Markern und ihren jeweiligen Werten. Manche Variablen, zum Beispiel Objekte, können nicht richtig angezeigt werden.]]></target>
+			</trans-unit>
 			<trans-unit id="backend.marker.type.array" approved="yes">
 				<source><![CDATA[Array]]></source>
 				<target><![CDATA[Array]]></target>

Resources/Private/Language/locallang.xlf

@@ -200,6 +200,9 @@ Please register your configurations in the according ext_localconf.php.]]></sour
 			<trans-unit id="backend.marker">
 				<source><![CDATA[Marker]]></source>
 			</trans-unit>
+			<trans-unit id="backend.marker.allFields">
+				<source><![CDATA[A table of all available given markers and corresponding values. Some variables can't be shown correctly like objects.]]></source>
+			</trans-unit>
 			<trans-unit id="backend.marker.type.array">
 				<source><![CDATA[Array]]></source>
 			</trans-unit>

Resources/Private/Templates/Mail/Index.html

@@ -57,6 +57,16 @@
 									<th><f:translate key="backend.description" /></th>
 								</tr>
 							</thead>
+							<tr>
+								<td>all_fields</td>
+								<td><f:translate key="backend.marker.type.string" /></td>
+								<td>-</td>
+								<td>
+									<f:translate key="backend.marker.allFields">
+										{backend.marker.allFields}
+									</f:translate>
+								</td>
+							</tr>
 							<f:for each="{selectedTemplate.marker}" as="marker">
 								<tr>
 									<td>{marker.marker}</td>