Merge tag '1.4.13' into develop

TextGrid Aggregator 1.4.13 can deliver plain text

The new /text endpoint can transform TEI or TEI Corpus documents to
plain utf-8 text and deliver that as single document. It uses the same
transformation that is also available in the ZIP export using
`&transform=text` for some time.

pom.xml

@@ -5,7 +5,7 @@
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>info.textgrid.services</groupId>
 	<artifactId>aggregator</artifactId>
-	<version>1.4.13-SNAPSHOT</version>
+	<version>1.4.13</version>
 	<packaging>war</packaging>
 	<name>TextGrid Aggregator Service</name>