Image thumbnails missing

@vmassol

I added it this way. Is it correct?

<Context allowMultipleLeadingForwardSlashInPath="true" containerSciFilter="org.apache.jasper.servlet.JasperInitializer">
  <JarScanner>
    <JarScanFilter defaultTldScan="false"/>
  </JarScanner>
  <!-- We need to set the resource cache size since the default (10K) is too small for loading all XWiki resources at
       once -->
  <Resources cacheMaxSize="50176" />
</Context>

If the code is correct, then this did not help, as thumbnails are still not shown.