Add vocabulary that lists all users.
Merge pull request #591 from 4teamwork/deif-advancedsearch-users

List all users in advanced-search when searching for dossier's repsonsible.
Moved DictStorageConfigurationContext to opengever.base.
Added option to disable download confirmation.
Catch up with latest changes on master, minor refactoring.
Add simple key-value store api.
Display portal message instead of 404 when attempting to download missing file.