Added version description, fixed loading version, added `react-externs`

Standalone `react-externs` component added to `bower.json`. Added attribute
description into each version file -> updated list of versions - date
formated and description displayed. Fixed loading of model from version.
Fixed for GCC compilation, added sending version content with list

Fixed assets, accessing refs, and `source` prop name to work correctly
after GCC compilation. Added sending content of version to client when
requested list of repo versions, so it's not neccessary to request it
with `get-version` anymore.
Adding versions into existing repo added, fixed diff at versioning

User now can display versioned schema, edit and add new version into same
repository. Fixed versioning with xdiff - each object in array (tables,
relations) had to had unique __id__ property, otherwise it doesnt work.
Added reverse order of versions, some small fixes

Versions are displayed in order from youngest to oldest now, added small
fix at reengineering dialog.