fix support for external assets

allows adding fast.fonts.com css to dependencies
fix includeCode with parentContent
fix uploads: add kwfSessionToken parameter
fix includeCode helper usage, fixes tests
improved security: timeout sessions after 20 minutes
output memory usage when refreshing cache
add hashed_directory_level to assets cache, many files can get generated
remove imageCaption from ImageEnlarge

- it is shown twice currently
- it's ment to be used for the thumbnail only
CSS File for animated loading images and IE fallback, not used yet
cache lifetime is set in seconds (just added a comment)