add mode='#all' to template, closes #45

the default mode is rarely touched in this Stylesheet since the initial match template at https://github.com/Edirom/MerMEId/blob/de50ec700d7eead0514d22fe601979e2a0ce437f/filter/xsl/filter_put.xsl#L37 only applies templates recursively in the "convertEntities" mode.
NB: This might be an issue for several other templates (e.g. "m:expression") as well!

filter/xsl/filter_put.xsl

@@ -41,7 +41,7 @@
     <xsl:copy-of select="$new_doc"/>
   </xsl:template>
 
-  <xsl:template match="m:music">
+  <xsl:template match="m:music" mode="#all">
     <xsl:element name="music" namespace="http://www.music-encoding.org/ns/mei">
       <xsl:choose>
         <!-- If no new content has been uploaded into <music>, reinstate the original content from the database. -->