first draft for #12

(just a draft for the handling at the admin-section)
fixed message keys in german file
#12 more workflow, changed form
added cleaner session-handling

additional memcached entries to map user's mail to a list of his sessions
-> all admin/user-actions (delete, activate/deactivate, pro-/demote user) will now be updated in the user-sessions
changed flash-message display in adminLayout

to have a consistent way of displaying flash-messages
#12 added workflow, value in application.conf, user-deletion, filtering,..
#12 added i18n-messages
#12 sorted the new message-keys
small typo
#12 handle no domainname-entries
Update messages.de.properties

textual revision Admin-whitelist section
Update messages.properties

textual revision admin-whitelist
Update messages.de.properties
changed Key adminRemoveDomain_Label_Description
#12 more doc, small fixes
small message-update
small design change
#10 confirmation when deleting accounts
Merge branch 'refs/heads/feature-12-DomainWhitelist' into develop